Warming sensation in penis which comes and goes for two years.had 5 urine analysis/std tests & cystoscopy all negative. what else could this be?

Nothing serious: No STD or other infection is a likely cause of such symptoms. It's good you were tested to be safe, but I would have stopped after the first negative results. The cystoscopy means nothing wrong with your bladder. Even if the symptoms continue and are unexplained, for sure you have nothing harmful. Some people just have to live with symptoms of unknown cause but do so easily once known not serious.