ויתרצצו הבנים בקרבה ותאמר אם-כן למה זה אנכי ותלך לדרש את-יקוק
The children struggled within her, and she said: “If so, why am I thus?“ [So] she went to inquire of Hashem
Rivka, the wife of Yitzchak, became pregnant with twin boys. These twins would eventually become Yaakov and Eisav. The Torah tells us that Rivka was having a difficult pregnancy. The children were very agitated within her. The next few words are phrased very vaguely. Literally read, it says that she said: “If so, why am I thus?” Rashi explains that what she meant was if pregnancy is so difficult, why did she even pray to conceive? She had been unable to have children for ten years, and her and her husband prayed profusely for her to become pregnant. Now it seems she was having second thoughts.
Perhaps there’s another way to understand what Rashi meant. We find something fascinating when we compare the conception of Sarah with Yitzchak, and Rivka with her twins. Rivka required a lot of praying to conceive. Sarah on the other hand became pregnant without any prayer at all. We know this because she was upset at Avraham for praying that he should have children, when he should have prayed that she have children as well. Why then did she merit a child? Some explain it’s because people suspected her of adultery with Pharaoh and Avimelech, the kings who abducted her into their private chambers. Miraculously, she managed to retain her purity. The Torah promises someone who is wrongfully suspected of adultery the gift of children. She merited Yitzchak due to this unjustified suspicion.
However, a surprising Midrash relates that immediately after marrying Rivka, Yitzchak suspected her of prior wrongdoing with Eliezer, Avraham’s servant. If so, since Rivka was obviously innocent, then she also should have deserved to conceive without the need to pray. Why then was it necessary to pray so much? Nevertheless, we find that the Torah not only promises a woman wrongly suspected of adultery with a child, it also promises a smooth and easy pregnancy and labor. Rivka knew this, and must have surmised that her prayers merited her a child, and the wrongful suspicion should have provided her a painless pregnancy.
Now we can understand her surprise that she was having such a difficult time. She knew she was wrongfully suspected in the past, and was deserving of some merit. Why wasn’t she having a smooth pregnancy? Even without her prayers, she should have conceived, due to the wrongful suspicion against her. The suspicion should then have provided her relief in her pregnancy.
She decided to seek spiritual guidance. She was told by a prophet that there were two nations in her womb. Besides all the above promises for a woman who is wrongfully suspected of adultery, there is also a promise of an increase in children. A woman who normally would give birth to one child, would give birth to two. It turns out then that while she didn’t merit an easy pregnancy, she did merit to be the ancestress to two great nations: the Jewish people through Yaakov, and the nation of Edom through Eisav.
 Based on Panim Yafos to Genesis 25:22
 Genesis loc. cit.
 Ad. Loc.
 This requires a discussion in its own right, as on the surface level it seems quite strange that Rivka would so easily regret her desire to have kids. The Panim Yafos will present an approach which avoids this difficulty See also Ayeles HaShachar ad. loc., who discusses if this regret made her lose any merits that she accrued for the mitzvah of having children
 The Panim Yafos cites this explanation from his father
 Genesis 16:5 with Rashi
 Bereishis Rabbah 53:6
 Numbers 5:28
 Yalkut Shimoni Chayei Sarah § 109; Midrash Aggadah to Genesis 24:67; Pirkei D’Rabbi Eliezer Chapter 16. See also Torah Sheleimah Chapter 24 § 237. This Midrash is brought by the Rishonim, such as Da’as Zekeinim to v. 39, Hadar Zekeinim to v. 63, Paneach Raza v. 67. See also Rokeach HaGadol § 319, Kol Bo Hilchos Kisui HaDam, and Rav Chaim Paltiel to Leviticus 17:13, who bring this Midrash as the reason why we cover the blood of birds and non-domesticated animals and not that of domesticated animals (although the Rokeach leaves out the part about Yitzchak suspecting Eliezer and Rivka)
 Berachos 31b, Sotah 26a, Yerushalmi Sotah 3:4, and Yalkut Shimoni Nasso § 709, brought by Rashi to Numbers 5:28. Berachos and Sotah bring these two promises as a Tannaic dispute (whether someone barren will conceive, or if they will have an easy pregnancy), but the Yerushalmi and Yalkut combine the promises as potentially possible
 Genesis 25:22,23. V. 23 says that Hashem told her. Targum Onkelos and Targum “Yonasan” translate it literally. Rashi however says that she was told by the prophet Shem, the son of Noach. Rashbam, Ibn Ezra, Radak, Chizkuni concur that she wasn’t told directly by Hashem. Perhaps they’re motivated by Megillah 14a, which doesn’t list Rivka as a prophetess. Indeed, this is what the Mizrachi says. The source that she was indirectly told is Bereishis Rabbah 63:8. The Mizrachi and Gur Aryeh also explain that since v. 22 says she went to seek G-d, that implies she went to ask someone what Hashem had to tell her. For a discussion if Rivka really was a prophetess or not, and the seeming contradictory sources on this topic, see Targum Onkelos to Genesis 27:13, Rashbam ad. loc., Maharatz Chiyus to Megillah loc. cit., and Torah Sheleimah Chapter 25 § 95 and 96
 The Panim Yafos’ father qualifies this promise by quoting Rashi ad. loc., whose source is Avodah Zarah 11a, that the two nations referred to here is a prophecy regarding Rabbi Yehuda HaNassi and Antoninus, the Roman Emperor. The footnote there explains this qualification is because it wouldn’t be reassuring for Rivka to hear that one of the two nations that she will bear will be a wicked one. Therefore, Antoninus is mentioned, because he was a righteous among the nations