Frequently Urinating. Please advise.

I feel my urethra full all the time. Had same problem before 8 months and went for sonography and blood report and nothing was found. Treated with one liquid medicine and got releif in two days. Now, i am havin same problem for a month, initially i consulted MD and he gave me 5 days medicine after checking Urin report which was very normal. I was feeling better but after 2-3 daya it happened again so i consulted specialist agaim and he gave me antibiotics for 20 days but no releif. Problem is minor and i can hold urine also for long  but its aanoying and feeling discomfort to have this feeling. I have to pee many times. There is not burninf sensation or any other pain while urinating. Please advise.