Could residual depo provera in my system be the cause of post coital spotting?

[jenrex]

I started birth control at 15 for heavy periods. I switched to Depo Provera after about 6 years on the same pill. I was on Depo Provera for 1 year. I stopped in December 2015 due to irritating light spotting and mood changes. I began BC pills that allow for a period only once every 3 months. The spotting now only occurs after sex or self stimulation. I got my period in February, and it was extremely light (not at all like I remember). I started the next pack of pills, still experiencing post coital spotting. I attended a gyn for a regular checkup, and they called for an ultrasound regarding the light spotting. It was found that my endometrium was at 15mm. They said it was extremely thickened, and required a D&C. As per my research, I found that this is not at all an abnormal thickness for when I'm about to start my period, so I disregarded it. During the exam they found that I had a minor infection or irritation with my cervix, and put me on a course of Flagyl. The post coital spotting stopped completely. A week later the spotting started again. It is now time for my period, and it's extremely light again... I thought that since my endometrium was "thickened", my period would thin it out, and I would just have a heavier period. If the antibiotics stopped the spotting, and now it's started again, but my period is light, what could be going on?