I Have Very Irregular Periods And I Don't Know Why.

I have very irregular periods and I don't know why. I had a miscarriage in May and I got a period about 5 weeks after. I found out I was pregnant in early February. My periods have ranged from 40-60 days apart since then and I've barely had any periods at all this year. I haven't been pregnant since but I haven't been to a Dr either. I am absolutely terrified of the Dr and I won't go, I just am really confused. I didn't go to the Dr during my miscarriage either, I have no idea how far along the baby was. I haven't even told a Dr. I just don't understand what's wrong wit my periods. I'm 17 years old, I am overweight but it's never mad a difference in my period.