What Causes Continuous Periods, Clots And Weakness?

hey. my period is continually. and now and then it stops for a few days. but around ones in a month the bleding gets so strong i have to stay home sick. the bleding is lumpy, and some of the lumps are as big as lemon. i have general felling of weaknes. the is amust Intolerable in the moment. i read i could be a high Level of Hormones, or even Cervix problems. beside telling me i sould see a doctor, Any advice?
im 18 years old.