Bleeding after menopause

Patient: I am 49 and have not had a period for the last 5 years and on hrt, for the past four weeks I thought I had blood in my urine as I had a stomach upset about 4 weeks ago and there was blood in my urine then, since then when I wipe it has been pink, but this morning I got up and went to the toilet and passed blood like a period from my Minnie, I went to doctors and they have referred me to gynaecologist in next 2 weeks and given me antibiotics for the blood in my urine, which apparently was a lot…what could be the cause of this?