Urge to urinate.

[pstrong]

I am a 21 year old male healthy, no known health problems.
Lately I have been having a wierd sensation at the tip of my penis, it feels like I am on the verge of urinating. Its hard to explain. It's almost like when you are just about pee and the urine comes out, thats what it feels like, and the only way to make it go away is to actaully urinate.
I don't have any burning, cloudy urine, or smelly urine, no pains, no other symptoms to suggest maybe an STD or an infection. It seems to happen right after I drink any kind of liquid, like it almost goes right through me. Sometimes it feels like I am about to discharge almost, and it doesn't build up or something it just happens and stays.
It seemed to happen right after I was with my girlfriend I will be graphic and honest ... I was uhhh excited when I was with her for sometime, and she had to suddenly leave, me quite disapointed in sexual acts, decided to have a few beers and watch TV. I ended up off my night masterbating (masturbating) while I was a bit drunk and I seemed to ejaculate prematurly. Ever since then I have had this sensation of me feeling like I am on the verge of peeing my pants.

I think it might be all in my head but I am not 100% sure, when I have an erection it goes away, when I'm not drinknig fluids it goes away. I am kinda lost, I will be going to the docters soon to get some tests done but I am just wondering if there might be an explanation.