I Have Recently Experienced Intense Pelvic Pains (period Like But

I have recently experienced intense pelvic pains (period like but much more excruciating) either spontaneously or after reaching an orgasm.
These pains last for about 5-10 minutes and I have to curl up and feel like vomiting. I have had two "series" (lasts for a week) of these.
The first time I had a series, I went to my gynae and I said that I think it's due to rough sex (traumatic cervicitis) or an std.
I took an std screening and was found to have chlamydia (everything else was negative) . My partner and I were treated (1 week vibramycin). And the problem seemed to be solved. I know I am free of cjlamydia because I took a secondary test- urine showed negative signs. My blood showed high antibodies. (Retested after 3 months).
However, now, I am having another series of these. And I think it's due to rough sex. Because both times I noted that my partner and I have had rough sex.
one other thing it could possibly be is my change from yaz (combination pill) to cerazette (progesterone only pill) in the last 6 months-both series of pelvic pains only happened within this time.
Other information: sexually active for 6 years. Only had 2 partners. But both were had many sexual partners in the past. I do not use condoms.
I want to know what it could possibly be- the physiology of it, what I should do medically and what I can do to avoid this.
Please help!