Tip of urethra looks red and swollen like a pair of lips. Please help.

[Miller2017]

I am 23 years old and uncircumsized. This has been going on for about a year now and im really getting worried as to what this could be.the tip of my urethra seems to look red or inflamed. It doesnt seriously hurt at all though. Whenever i do pee, sometimes there is a slight tingling/burn at the end of urination but it isnt any serious pain. Over a year and a half ago, i did stupidly recieve unprotected oral sex from a prostitute but about a month or so after, i did get a urine STD test and the results came back negative. This inflamation or whatever seems to gradually get a bit better and sometimes it gets worse. Mostly after masturbation is when it really looks irritated and not normal at all. There is also a slight tingling after masturbation where this is but eventually it goes away. Ive been to the doctor and he looked at this and he says it doesnt look too concerning and maybe its because of my penis head rubbing up against some clothing. But wouldnt it go away by now? Its been a long while since ive had this and if it feels weird after masturbation, something must not be right imo. Could me being uncircumcised have anything to do with it? I am also afraid that it might be some kind of disease/STD even though a month or so after that encounter, i got tested and came back negative. This is really worrying me because it just doesnt look normal at all.