I have had this happen - mostly around ovulation and right before AF and when I was really pregnant.
I have heard maybe this might have something to do with progesterone but I have also seen online a whole host of other less healthy reasons that this could be happening like because of endometriosis, PCOS, PID, cervicitis, etc. etc. etc. - if you google "tender cervix" or "pain during intercourse" you can find lots of ideas to explain cervical tenderness or pain like:
|Probably not the cervix causing the pain. The cervix has few if any pain fibers. Moving the cervix will stretch the fallopian tube and cause pain if the tube is inflamed. Around the time of ovulation, there is increased vascularity in the pelvis and this could lead to some tenderness with intercourse.
Or if you really want to freak yourself out
you can look at sites like this
: I tend to try to avoid doing this too much though....its pretty scary and I don't like going to the OB/Gyn....you can also search mothering for more natural remedies (especially on the health boards) if you suspect an infection....