What Causes Stomach Pain And Tender Breasts While On Clomifene?

I am 26 years old with a 5year old boy. I have been sexually active ever since I gave birth but I havent got pregnant again.My doctor gave me Clomifene which I took 2 days after my periods at the start of April for 5 days.My next period was to be last week but I didnt get.I took a pregnancy test but it was negative.I feel stomach aches,my breasts ache and mild backaches. Could it be side effects of Clomifene?