Why Did Rachel Blame Her Difficulty In Having Children on Yaakov?

I don't believe she really did on a rational level, but rather that she was frustrated, and was venting. And Yaakov was not really criticizing her in turn, but rather was frustrated and was venting as well. This is all happening on an emotional, rather than a rational level. The psukim:

א וַתֵּרֶא רָחֵל, כִּי לֹא יָלְדָה לְיַעֲקֹב, וַתְּקַנֵּא רָחֵל, בַּאֲחֹתָהּ; וַתֹּאמֶר אֶל-יַעֲקֹב הָבָה-לִּי בָנִים, וְאִם-אַיִן מֵתָה אָנֹכִי.	1 And when Rachel saw that she bore Jacob no children, Rachel envied her sister; and she said unto Jacob: 'Give me children, or else I die.'
ב וַיִּחַר-אַף יַעֲקֹב, בְּרָחֵל; וַיֹּאמֶר, הֲתַחַת אֱלֹהִים אָנֹכִי, אֲשֶׁר-מָנַע מִמֵּךְ, פְּרִי-בָטֶן.	2 And Jacob's anger was kindled against Rachel; and he said: 'Am I in God's stead, who hath withheld from thee the fruit of the womb?'
ג וַתֹּאמֶר, הִנֵּה אֲמָתִי בִלְהָה בֹּא אֵלֶיהָ; וְתֵלֵד, עַל-בִּרְכַּי, וְאִבָּנֶה גַם-אָנֹכִי, מִמֶּנָּה.	3 And she said: 'Behold my maid Bilhah, go in unto her; that she may bear upon my knees, and I also may be builded up through her.'
ד וַתִּתֶּן-לוֹ אֶת-בִּלְהָה שִׁפְחָתָהּ, לְאִשָּׁה; וַיָּבֹא אֵלֶיהָ, יַעֲקֹב.	4 And she gave him Bilhah her handmaid to wife; and Jacob went in unto her.

Still, Ralbag (see image to the right) has a different explanation, where he seems to assume that she had some rational reason for her words and "accusation."

Thus, Ralbag first suggests that she suspected that Yaakov truly was at fault, and that he was, perhaps deliberately, holding back children from her. How so? Coitus interruptus, that is dash mibifnim vezoreh bebachutz, or something similar to this. And this is why Yaakov responded with such hostility to an accusation otherwise (I would say) simply leveled in anguish.

Indeed, I would point out that this idea is not without basis. For example, Lemech was the first with two wives, and the midrash criticizes him, saying that he had one for children and one for beauty, such that presumably practiced contraception with one of them to preserve her beauty. And indeed, IIRC, this was also what a midrash states Er was doing when he practiced the same, to preserve her beauty. Considering that the pasuk relates that Rachel was very pretty, and that he loved her more than Leah, one could argue that this is what Rachel suspected Yaakov of doing -- having children through Leah, and keeping Rachel for her beauty, and thus taking steps to preserve it. Ralbag does not suggest the above, but I am just fleshing out the idea. Indeed, according to Ralbag, Yaakov wanted Rachel more because he thought she would produce for him healthier offspring than Leah, who seemed to have some sort of eye disease (see earlier in Ralbag.)

Then Ralbag offers another suggestion, and states that he thinks this is preferable, that Rachel knew the power of Yaakov, that he could give her some advice, al tzad hachochma, via wisdom/science, about how to succeed. And then Yaakov grew angry and her and responded as he did, that it was Hashem who was withholding it from her.