I Have Had Severe Periods 3 Times This Month, Every

I have had severe periods 3 times this month, every time my tailbone hurts to a point where i can not stand and ches not stop, my abdominal is always swallen. my periods start with dark black like blood and end with thick mud like substance. am suffering and need answers I can't continue in this pain. I had a c section 6 years ago and have had 2 cycles a month since then. the pressure in my tailbone and ache in my side is excoriating . what is wrong with me please please help