Really bad period cramps, symptoms and pain!

I have been having really bad cramps and back pains during my period. The back pains feel like I have been slouching for my whole life. Cramps feel like someone took a knife and decide to stab me through my vagina and leave it in there till it reaches my uterus and decide to punch after that. I usually stay once a month at home from school to deal with the pain when its cold the pain gets worst. Blood clots are huge the size of a quarter or a golf ball. I had my period since I was 12 years old and now I'm 18...I hate that I can't deal with the pain...