what can cause this? have you had it before?

First of all before everyone starts telling me to go to the doctor and get check yes I have went already and discussed this with my doctor but I don't have my next appointment in till may 15 . So let me start , 2 months ago I was worried because I wouldnt get my period and I thought I was pregnant so I took like 6 pregnancy test all of them where negative I was late by 2 weeks which I have never been that late . This month now I got my period a week early it was kinda like spotting I wouldn't fill up a pad . My period usually only last 5 days but ever since I got it till this day it hasn't stop I have it now for 3 weeks almost a month now. I will sometimes bleed not that heavy and sometime it's a less kinda like spotting and some days I'll have clots rate the time I do . 2 days ago it stoped and was bleeding brown and today I'm bleeding again and know it's like normal period but not heavy . I just went to the Doctor on feb 15 and I talked about this with my DR but she told me it might be my hormones unbalanced or bcuz I'm overweight but I honestly don't think it's bcuz of this I have always been overweight and it has never happen . Now let me say this I did had a miscarriage back in may 25 at 5 months pregnant and I know after a miscarriage a period can change but once I had the miscarriage my period was back to normal like always . My period bearly started changing 2 months ago . Can you guys please help me or know anything about this I'm kinda scared . Thank you in advance . (I'm 19 years old)