Drops of urine remain in the penis after urinating

After I urinate (pass water), some drops or urine remain in the penis and I sit in the bathroom for a quarter of an hour to clean myself properly. Of course, this is very tiring and exhausting for me. After that, I do wudoo’ for prayer. I have been to a number of doctors, had tests and taken different kinds of medicine in an effort to solve this problem, all to no avail. After I clean these drops of urine, I do wudoo’ and go and pray, but during the prayer I feel as though there are still drops of urine in the penis that need to come out. Of course, this is giving me trouble and causing me embarrassment, especially when I pray in jamaa’ah (congregation) and then discover drops of urine which did not come out when I was sitting in the bathroom, so I have to repeat my prayer, or I doubt that my prayer was valid. Please help me with a clear fatwa.