Bleeding during clomid cycle

Gillian
I have pcos so had to take provera to start a period. When I started bleeding I started on 100mg of clomid. But yesterday was day 18 for me and I started to get cramps then I started bleeding red blood. 
​I am confused as why i started to bleed half way through my cycle as I was due to get my day 21 bloods on Monday. Has this happened to anyone else? Please help.