Any advice

I got pregnant when I was 18 was into the first week of my second month and I had a miscarrige. I got the depo shot every three months and only got it 3 times. I am now 21 and me and my husband have been trying for 2 years and nothing. Ive tried the period tracker app now im going to give this a try. Im hoping it works out but any advice is good. Ive been to my Drs. they said theres no reason I shouldnt be able to get pregnant. Ive been checked for STDS and all are negative the only thing I can think of us cyst so I that may be the cause but I dont have them all the time and they go away on there own (as the Drs. say) sometimes I spot and am late for my period so I automatically get my hopes up but then I get the let down. Please help