2 week long period :(

I started the pill about 5 weeks ago, basically on the first day of my period before this one. The doctor told me that this particular pill would stop my periods and it has done the complete opposite. This period has lasted 2 weeks now and it's not even blood, it's brown and contains big clots. So I'm just worried and wondered if anyone else has experienced this. 
if it helps it's called desorex and it's the 4 week one which you take every day.
Please someone help :(