Hi,
i'm on my 2ww wait as well. On day 9. Just had my 2nd IVF cycle too.. and I have had back pain... I didn't have this on the first cycle either.
I started with strong cramping after the transfer for several days.. It lessened but started to feel like my AF was coming.. Now I have no cramps, just bloating, tired, lower back pain and swollen bb's... (not as sore as the beginning)..
I know the progesterone/estrace can cause some of these symptoms too.
Here's to hoping the back pain means pregnancy!!! I go in for my Beta on 10.4
I'm not sure where you are in your cycle, but I can tell you that before I got my BFP my back hurt soo bad. It was the only strong pg symptom I had, especially if I leaned a certain way, it was like a sharp spasm of pain would shoot out from my lower back out to my hips. Good luck! :0)