Getting pregnant

So me and my fiancé are trying to have a baby I was on the depo shot for almost four years before I got off it. I have tried everything to jump start AF. It’s been almost four months and no period! But I have one day a month I bleed super heavy and then it’s gone the next day. Not sure if that is a period or what. I just got a faint positive pregnancy test this morning. But I have problems when I do get one blood work comes back negative. Any advice would be appreciated. I have been tested for pcos and I don’t have it.