I masturbated today, I urinated about a half hour before I decided to masturbate. So just before going to the bathroom, I had pains like I had to pee, like my stomach hurt, even though I just had peed. So when I did masturbate, the pain was bad and as I ejaculated, it seemed as though it was urine that came out instead.
So I kind of freaked out, I don't know if this is OK, cause it hasn't happened before. So I've been drinking water like crazy to flush my system. I seemed like urine instead when I ejaculated, it didn't feel the same as it usually did.
Does anyone know what's going on?

*Edit*
I just went to use the bathroom again, and I urinated but it keeps feeling as though I need to urinate again, and It feels like my kidneys are paining(unless this is just the pain in my stomach radiating to my back) but while I urinated, it was a constant flow(clear this time though usually yellow for me) but, this may sound weird, I kept peeing but then stopped and then went again for a very tiny bit, and stop, then another tiny bit(almost like ejaculation pulsations). This is really freaking me out, cause I read that you can't pee while masturbating cause a "valve" shuts off the urine. Could it be how I tried to masturbate earlier, but was interrupted when someone came to my room, then stopped for a bit then tried again(3 times). It didn't look like there was any in the toilet while it happened, just kind of looked like a clear liquid shooting out, and I didn't have to squeeze any excess out of my penis.
Like to push in on my stomach now, it feels like there's urine still there, my bladder hurts, and if I go to pee, the same process of the flow starting and stopping I'm guessing will start again.
The pain that I feel in my stomach is the feeling you get when you strike your testicles, and if I touch them, they're sore now.

I'm like freaking out, I have no idea what's going on? Should I take some advil/ibuprofen?

There are several things that could be going on. First, you could be trying to pass a kidney stone. Second, you could have the start of a kidney or bladder infection. Third, is prostate gland problem. In any case, you should see a doctor or urologist as soon as possible before the problem gets worse.

I took some Advil, and the pain has gone away. I'll keep an eye on it for now, and if it gets worse, then I'm gone to the doctor.
Should I refrain from masturbating for a few days, or should I try it again tomorrow to see what happens?

I'm glad to hear the pain is gone but the thing to watch for is the stop and start urination you mentioned. If you urinate then 5-10 seconds later you feel like you need to again, that could be a prostate problem. The prostate could be swollen and interferring with the urinary flow. The prostate is the valve that opens to allow urine flow or if ejaculating, it shuts of urine flow and opens to semen flow. When you mentioned that it was urine coming out when you masturbated, my first thought was you may have a prostate problem.
I've had prostate infections in the past (prostatitis) that almost completely blocked off the urine flow. If it is a prostate problem, then I would definitely not masturbate and irritate the gland any further. Also, if you have a burning sensation in your uretha, that is sign of infection which again could be kidney, bladder or prostate.
If it starts getting worse, get medical attention asap.

OK then, I'll refrain from masturbating for a while, but all of the urine is gone from my bladder now. I think the ache in my back was from slouching in my chair while on the computer because it only ache when I'm on the computer now.
I didn't have any burning sensations, I had a UTI a few years back, so I know how they feel, and they're not good.

I will say that a back ache is how my kidney stones always start, and it slowly changes to feel more like a knife in the back

Sounds like a kidney stone to me. Mine started with back pain and finally before it passed I was having to go to the bathroom ever 5 minutes.

I've been perfect the whole day today, no pain whatsoever, like nothing happened. Though I'm still going to stop masturbating for a while though just in case