Burning sensation on penis

So, I have this very annoying problem which seems common but I haven't found a good answer yet. Sometimes I get a burning sensation at the tip of my penis. It's very rare and it never occurs exactly, however, it does almost always occur when I pee and take a dump at the same time. It's like you got a needle stuck in it and it hurts. Just now I checked, so, in the foreskin there was quite a bit of fluid (Logically, cuz I just peed) now, I also pulled the foreskin back and noticed there's a red line across the peehole. The pain is gone now but can anyone tell me what causes the pain and possible what the red line is? Some health info;

- I never had seks

- I masturbate an average of 4-5 times a day... (I'm still in puberty)

- Also keep my pants on with it

- I don't use any medicine

- I also never pull back the foreskin... Mainly because since I was a kid, it hurts when washing the little thing, also heard you've got to wash with soap, seems painful...

Any help is appreciated

I believe the nerves in the prostate and at the end of the penis are linked, and so when there is some pressure (eg from faeces in the rectum) it can be felt at the tip of the penis. Either that or maybe your urine is rather strongly acid or alkaline depending on what you have eaten and drunk. The fact that the burning sensation passes suggests it is not a serious problem. 

If you're masturbating with your pants on I guess you risk chafing at the tip. Maybe it would be wise to do it naked.

Pulling back the foreskin is important when washing - preferably without soap, just water.

Masturbating with your pants on sounds very strange.  How old are you?  Don't you ejaculate yet?

As Pepasan said, if you can pull back the foreskin, you should, so you can wash it.  Just with water, not soap, and it shouldn't be painful.

If you can't pull it back, then depending on your age, it might be something you should see a doctor about.

@Pepasan

I think my urine is just strongly acidic because I drink A LOT of coke in one day

Yeah, I guess

Oh so without soap? Alright, I'll try tomorrow, hopefully it won't hurt

@ml66uk

I do it because 2 reasons: 1) I'm used to it so it's very easy 2) Porn is clicked away easy... putting pants back on quickly not (still live with parents)

Alright, back in the day my mom forced me to do it with a bath cloth which stung, so i haven't done it for years anymore