What Could Heavy Menses During Depo Shots Suggest?

I usually have really heavy periods but I started 2 days ago and it s very light. I was on the depo shot and had a constant spotting 7 months after the shot. But shouldn t my periods come back to normal? I also took like 6 pregnancy test, which 3 came back a faint positive and 3 came back absolute negative. What s really going on?