Can Yasmin Cause Cramping And Discharges Outside Menstruation?

I'm on Yaz I'm now in my second week taking it in month 4. I had a normal period the first month, brown discharge the second and no period, a very heavy clotted period the 3rd month and now i have period like pains two weeks into taking the 4 month. I have taken 2 home pregnancy tests and a blood test and am not pregant, so why am i cramping up now and have had brown discharge instead of a period? I am also getting headaches nearly every day and rotate between Constipation and diarrhea.