Why is my period light and then heavy and when its light I get clots? I have been 4 an ultra sound and nothing? I am 35yr old

May be normal. There is no "normal" menstrual flow other than overall amount and duration. If you are not changing pads or tampons hourly and your menses are up to about 8 days total, then this may be what your flow is now. It may change in the future. A woman's menstrual flow is not the same her entire lifetime. Clots are not by themselves significant.