"2nd time on the Depro Shot at 20"

I'm 20 and this is my second time on the Depo shot. The first time,I was 16 and I gained tons of weight. I'm 20 and married now. I've been pregnant once and went into midterm labor with my twin boys.I've been back on the shot for about 3 weeks. I regret getting it again. Because I don't know if I will ever get pregnant again. The second thing is,before I got back on the shot,I had an extremely heavy period. It suddenly stopped and now about 4 weeks later,I have a period. I think I may have had another miscarriage,but my doctor said everything was normal. I'm definately nervious about not being about to get pregnant again,even though I am young. I want to give my husband at least one child.But what do ya'll think about this little period? I didn't have a period the last time I was on the shot.Where do you all think this could have come from? My doctor really isn't a big help either. I'm thinking about fertility pills or some type of treatment. Can anyone recommend anything?