Help? Am I fertile?

So I got on depo in Jan. April when I was supposed to get a new shot I never did. (purposely due to heavy weight gain!) I didn’t get a period until July 6. Then got one August 3. It’s Sept 3 and I’m currently three days late. Do y’all think it’s because of the shot? I took a cheap corner store pregnancy test the first day of my missed period and got a negative. I don’t think I’m pregnant (I keep having cramps like AF is coming but it’s a no show!) and I never had irregular periods before the shot, so does anyone know what’s wrong? any advice/help would be appreciated!!