Suggest Treatment For Blood In Urine

I had turp on June 10, 2010. My urine flow has improved a lot. No urine block.But I have to go two to four time for urination in the night.In the month of February 2011, I saw blood and blood clotes in my urine. My urologist checked my urine and found no infections. After about 10 days, there was no blood or blood clotes in my urine. Then again after one month, I saw blood clotes in my urine and again after one week urine was again clear. Then after two weeks, I again had blood and clotes in my urine. But now again urine is clear. I am taking lots of liquid as suggested by my urologists. My body weight is normal as well as other vital signs are okay. The bleeding in urine appears after a day or so going for biking or running. I have now stopped biking or any heavy exercise. Any advice that can prevent bleeding will be greatly appreciated.