Irregular period

I was on birth control for about 5 months before I stopped because of certain reasons. When it was time for my period to come, it came, but it was really light, lasted 3 days when my typical period length prior to birth control and during was ~6 days, almost like spotting. But I thought it was my period.
Then two weeks later I was having sex and as soon as we finished, I had this really bad pain in my lower stomach which I googled and found it to most likely be pelvic pain due to intercourse. I had no idea why this happened to me when I've been sexually active for almost two years.
Now, a day after that incident I got my period again. It is still sort of light, but I'm confused as to whether this might be a sign of implantation bleeding, or just because of my birth control/body changes. Help!