Pain in the base of penis shaft and testicles (Age 21)

[anon92834]

So a few months back I accidently sneezed while I was urinating. The pee stream abruptly stopped but continued after a few seconds. About 10 min later my testicles and groin started paining and quickly got worse to the point I couldn't walk for a few hours. The pain subsided eventually but the problem didn't.
Now this is the important part.
Whenever I went to pee after that, sometimes right after finishing I get a feeling of "backward motion" as if something went back. If this happens, it will pain again. I had to carefully pee while sitting to make sure that "backward motion" at the end of unrination doesn't happen.

I went to a doctor and he said its nothing serious, that I probably sprained my nerves and gave me Urispas. I took that for a week and the problem ended.

Or maybe not, because a week back I got the same pain in the same spot after I masturbated. Now I have been masturbating regularly for years(2-3 times a month), nothing out of ordinary but I have noticed that my masturbation is triggering this problem (described in the first para).

The pain is bearable when I'm sitting, but intentifies when I walk or stand. The testicles pain if it touch them, so I don't wear any tight undergarments.
When the pain is at its peak, even my lower abdomen and lower back pains but usually its confined to the base of penis and testicles.
Absolutely zero issues with urinating or urine itself. No pain in the penis or ejaculation either.

I need to know if its not anything serious.