Your symptoms sound very similar to what I had. I bled exactly 3 weeks out of every month, one week off and three weeks on again. Lots of clots, too.
This went on for many months. So did the bloating and huge stomach. I had a fibroid tumor (one large one--most people have clumps of them) that was causing all of this.
This was 9 years ago and I wanted a myomectomy (just removal of the tumor) rather than a hysterectomy. It took me a year and a half to find someone willing to do that surgery. Even the hospitals involved would schedule surgery, then call me the night before and say, "Hysterectomy or nothing."
Now that more people are opting for myomectomies, they are probably easier to get.
Dr should be able to feel fibroids readily, but you may need a sonogram.
Could be fluctuating hormones. Peri-menopause causes similar symptoms.
Best of luck,