What Is Causing Spotting Of Blood After Urination?

Hi, Im a 24 year old female in australia. I have a child that i gave birth to naturally 6 years ago (if that s relevant) Recently, i found blood in my urine. Or more precisely, following urination. So my urine looks clear but when i wipe there is a big spot of blood. This was happening only at night and in the morning every day. I had a urine sample taken but it showed no blood in the urine itself. I checked myself to ensure it wasnt a vaginal bleed and it 100% is not. I also checked to ensure it was specifically coming from my urethral orfice. This lasted about a week (daily) and since then it has happened maybe twice in the past 5 days. I also seem to be excessively belchy. What could this possibly be? My dr has no clue. Ive been sent for an ultrasound but just wanted a second opinion because im getting nervous! Also, i have had no associated pain besides being tender from bloating which i assume is associated with the gassines. Thank you!