Period problems

I don't know what is wrong with me but my period is sooo screwed up. I haven't had a period since March 13th and I don't understand why. Normally my periods are two months apart but sometimes I go as long as 4..I know  not pregnant. I've taken tests every other day because I'm trying to get pregnant....and I have spoke to my dr and she keeps saying it will happen. Anyone have any similar situations?