Had 4 faint lines- then started a week late

I see all these pictures of faint lines and everyone says they are positive. Every test I have taken in the last 4 months has been like that, but a few days after my missed period I end up with a very heavy period. Like I said the last 4 months. This last month I was a full week late and thought I was definitely pregnant then started. Any idea why this is happening? Am I miscarrying when this happens!? Please help I'm going crazy!