On 8th day after last provera (medroxyprogesterone) pill (10mg/10days) no withdrawl bleed yet. Def not preg. But having sore breasts after last pill. Period on its way?

Possibly! If no withdrawal or delayed beyond this time then it's not Provera (medroxyprogesterone) eliciting a response.This could mean menopause approaching or other conditions : e.g. Thyroid disease occurring.