3 months of Prostatitis. Please advise.

Hi, I have been suffering from Penile shaft pain from last 3 months, pain is on and off, however it mostly comes after urination and ejaculation. Consulted couple of Urologist, examined and concluded Prostatitis. They have put me on 1 month long 100mg antibiotic (Doxytop) once a day regime. One doctor have asked me to go for 250 mg antibiotic, once a day for whole month, but couldn't continue the course as I have IBS which already got aggravated while finishing the Doxytop course. But after finishing Doxytop antibiotics course, have no relief, have also done lower abdomen Ultrasound, blood test, Urine culture and Routine urine analysis, all have come within the range. Now little worried about it as what I should do. Please advise.