What Causes Heavy Menstruating Periods With Blood And Clots?

I am 28 years old. My periods are quite heavy. I read about how much is normal. During the first 2-3 days I can pass up to 10 tablespoons of blood a day. i need to go to the toilet very often (every 1-2hours) so I could push out blood and blood cloths. Otherwise blood would leak out when I walk or get up quickly. When I do go to the toilet regularly and push things out, it is easier to cope and i am not leaking too bad. In the morning i have to rush quickly, sometimes messing the floor. I used to have very painful periods when younger, now i can cope without pain killers. sometimes have short abdominal cramps and pains during the perdiod and other days. my periods lasts 7 days. 3 of the last days is light periods or spotting. cicle is around 26-29 days. I always had heavy periods with blood cloths, but for the past 2 periods blood is very thin, almost watery, with lots of cloths as well and heavy. i can easily pass a tablespoon each time when i go to the toilet. i read about endometriosis, cysts, ovarian cancer....can it be normal what I experience? I never been on birth control pills, trying to conceive for a long time. never was pregnant. PLS help.