Why Is My Period Heavy Then Light Then Heavy Again

There is no normal menstrual flow other than overall.
Why is my period heavy then light then heavy again. For the past two months however my period has been light. Heavy then light periods. I have been 4 an ultra sound and nothing. I went to the gynecologist yesterday who seemed to think.
Light period then missed period. Heavy cramping light period. Instead of my period i had brown spotting on toilet paper only twice over a two day period. I am 35yr old answered by dr.
I have veins in my b sts but all my tests are negative. This month it seems to have only lasted two days and was light with some cramping. Why is my period light and then heavy and when its light i get clots. This month when it came it was really light day 1 and 2 kinda light day 3 and almost gone day 4 with a little spotting day 5.
For the first time since i ve had it my period came 2 weeks late and was really light. I had s x a week before my period. It sounds like a typical irregular period. I had very large clots and a lot of blood.
It usually runs 5 days heavy day 1 2 tapering off 3 4 and almost gone on 5. Then being 10 days late i had two days of bright red bleeding and then pink spotting then nothing and then pink brown. Was very short period. Why is my period light then heavy.
Heavy period then late period. Send thanks to the doctor. Period 1 week early brownish discharge then heavy bleeding my period becomes very light for a few hours and then it just becomes heavy again blood clots and heavy bleeding after intercourse heavy bleeding after getting off depo had heavy period for over two months clotting and light cra no periods for 6 months and then sudden bleeding.