1 month long period, not in birth control

Has anyone had periods for a month? I've had slight bleeding for a month and it's very light and I really don't cramp. I also sometimes bleed  after a bowel movement and then don't bleed at all during the day. I do feel bloated sometimes but that's about it. I've gotten an ultrasound done and it came normal. I am very overweight and have a BMI of 40. Doctors keep telling me just loose weight and I'm trying along the way I keep getting stressed something is wrong. I am 20 and never had sex.