Irregular periods, brown spotting, prolonged bleeding.

I've been battling irregularity in my menstrual cycles for a while now. First it was a couple months with no period at all, then brown spotting that went on for 6+ weeks with no actual bleeding. Then I went a week with no spotting, followed by a two week period with "normal" bleeding (red, reasonably heavy flow) that gradually tapered off after the first week. Now it's been about five days, and after an orgasm this morning, I noticed blood again, as though the orgasm itself set loose another cycle.

When I'm menstruating normally, I have pretty nasty cramps. Throughout all of this, however, there's been no cramping at all. I'm not on birth control, nor have I been for several years. I'm 99.9% certain I'm not pregnant. I'm overweight, and stressed. Could that be what's causing all this? Or should I see a doctor?