Thanks for your comments ladies. This pain (and I'm calling it that because in the beginning it was much more than tenderness - haha) started the the day before I started the Prometrium so you're probably right Heather that it's a combination of ovulating and the medicine itself. Why is it that the days seem to go by so slowly when we're waiting for the next cycle to being?! :)
I had a lot of breast tenderness last month bc I was taking prometrium and esterdiol, when I told my doc she said prometrium was causing it, this month I'm only taking esterdiol 2mg a day and I have extermely sore breast again. Not sure if it's due to esterdiol or I'm pregnant.
Sorry about the cancelled IUI. It's most probably the progesterone that is causing the tender breasts. I always get tender breasts after ovulation when progesterone goes up. Prometrium is a synthetic progesterone, so that can cause breast tenderness in and of itself...and then, if you ovulated, the follicles you had will produce progesterone, as well...so the levels are most probably much higher for you this cycle than normal. It should subside at the end of the cycle.