Why Am I Bleeding From Past Four Weeks?

I have been per ripped utolvan as I have been having bleeding I m post menopausal taking Premique Hrt I had a pelvic ultra sound in May which was normal and a routine smear was negative today my GP also did an internal examination she seems to think its a hormone in balance ?. Plus I was given antibiotics a couple of weeks ago as at first it was thought it could be a waster infection thus proved negative too. I ve had the bleeding now for approx four weeks