It would be interesting to take a poll on overweight women to see if his theory pans out! I have heard this theory said before but I think you have to be REALLY - REALLY obese for that to happen. I was once 300 pounds. I never had spotty periods. Two of my sisters are heavy, and I've known many heavy women. None of them had irregular bleeding, with the exception of 1. She had fibroid tumors (which cause extra bleeding).
Let's look at this logically. If your doctor's reasoning was correct then wouldn't most, if not all overweight women have abnormal periods? Conversly, all those slim ladies wouldn't have a problem with spotty periods either, right?
It's a shame that your doctor, with the plethora of medical tests that he has at his fingertips, could so quickly blow this off as a weight issue without ruling out some other things first. Abnormal vaginal bleeding SHOULD ALWAYS be further evaluated. In fact, I don't know how old you are, but the American College of Obstetrics and Gynecology recommends an edometrial evaluation on any woman 35 + who has abnormal uterine bleeding.
Health issues that can cause irregular bleeding:
pelvic infection, endometriosis, fibroid tumors, ovarian cysts, uterine polyps, steriod therapy, cervical or uterine cancer, ovarian cancer, adrenal tumor,hepatic disease, leukemia, pituitary adenoma, Hormone imbalance, indoctrine issues, malfunctioning adrenal glands; adrenal hyperplasia, Hypothyroidism, renal disease, failure to ovulate, perimenopause, diabetes, and medication side effects.
Since your doctor is not willing to take an active role in your health, I would get another doctor. I'm not trying to be an alarmist, but the number one symptom of 'female' cancer is abnormal bleeding - usually heavy bleeding. Why not double check everything just to be on the safe side. Ask them to give you an ultrasound as well.
I would second the motion to get in touch with your body and start charting your ovulation cycles.(book:taking charge of your fertility.) Sometimes we can miss ovulation, that's true, but that much.... seems excessive. Second, I would go online and invest some time in medical research. I like the site wrongdiagnosis.com. Also, search out sites on abnormal bleeding, candidas albicans and thyroid malfunction. Eating the wrong foods can cause a candidas overgrowth that can cause thyroid/hormonal problems. Candidas causes cancer. Large amounts of Soy can affect hormones. Vitamins that are in the foods we eat assist in hormone formation, so foods that lack adequate vitamins can whack your hormones. Adjusting your diet would be a smart thing. take Vit. b complex (sugar destroys vit b) vit c and cod liver oil. Try to reduce carbs. Low carb diets help to keep candidas in check.