Hi I Was Wondering If You Could Help Me. I've

Hi I was wondering if you could help me. I've changed to the pill from the implant 4 months ago and I had a really moody week when I was suppose to be due on 1st of October but nothing came. My boyfriend returned from tour and we had sex how ever the week leading I had what I'd call on off period cramps. Now 2 days after sex I've almost a continuous pelvis ache and feeling abit sick...... I did a test to make sure I wasn't pregnant but came up negative. Someone said if your not sure when your periods are provided there irregular you need to wait 5 days to know ........ help lol I don't like this continues ache is it just adjusting to my pill ?