Yeah, I had that happen at about 3 1/2 years on T...monthly. Quite unpleasant

Resulted in surgery for me. Turns out I had a HUGE benign tumor attached to the backside of the uterus. While relieved to have all of those things removed from my body, I had not really planned on it, and the procedure had to be done abdominally, which was a difficult surgery and recovery. Light bleeding happens to many people after some years on T and then goes away without incident, but I would probably get it checked out though, as it could be something more serious.