I always get crampy after sex. Nothing severe, but my stomach gets hard as a rock. I hear that's from having an orgasm. I guess another way to know she's not faking. Lol jk!! Maybe speak to your doc about it just to make sure. Congrats and good luck!!
I have read that it is normally recommended not to have sex in the first 2 months especially if there are severe cramps.
Cramping can be common after sex. You are early on so I would maybe mention it to your gp. Just to hear it from a professional for that reassurance. Congratulations on your baby :-)