What Causes Thickened Uterus?

I am 52, had thermal ablation 4yrs ago for heavy, non-stop bleeding. Cervix scarred shut, I am still having bad cramping almost every month, but no bleeding. Also begun bouts of painful urination in the past year. I just had a transvaginal ultrasound which showed a thickened uterus. I think I will need an endometrial biopsy to check for cancer, but I am worried about this being painful due to the scarring. Should I be worried about cancer, and how can they get a biopsy?