Cycle

So my last period lasted over a month I had the heaviest flow with large blood clots which I’ve never had before. I’m currently have the nexplanon implant in my arm (3 years in October). I went to the doctor and they basically blamed the irregularity on my weight. Tested me for STD which came back positive for chlamydia. Which I got the meds and it’s been 2 weeks since I took the 1 time dose. I once again started my cycle last week bleeding super heavy with big clots. At this point I don’t know what to do the doctor doesn’t believe me when I say something isn’t right. And i have never bled this bad for this long ever before. I know it’s not just because of my weight. I’m only 20. Help ?!?