Recurrent urination problem. For good?

I'm just 25 & all of sudden since last year once and then mainly this year around April fist, then September and then since 3 weeks into November i have been having this urge to urinate again & again, &the feeling that something's left in the stream which urges me to go again! I have done all the tests from KUB, Urine culture, Semen culture & they all have come out normal then why am i having this problem? I have consulted a few doctors too, one said its OAB so i was advised mirago 50 for 10 days first, so i had it for a few days and the problem stopped in September! Then again after a month the problem began again around October end & still on! One doctor advised me an urodynamic study while another has told me to have backstol 200, alfoo and mirago 50 for two weeks and observe! I didn't want to get the urodynamic study done as it looks quite scary & I'm just 25, so i have started with these medicines but is it safe? What should i do and end this problem for good? Please help!