I wouldn't worry about it if the tests came back negative. Mine were negative too. I think the tip of the penis can get inflammed and permanently enlarged after a rough handjob or ******* and that it just takes a long time for this to subside since the new exposed skin gets irritated so easily. it's been over a year and most of my symptoms are gone. However, my penis still looks uneven, and I still can't wear boxers and comfortably move around. But I'm 99.99% sure I don't have any STD.
I've had similar issues after a rough handjob. My meatus has looked strange ever since, almost as if it has folds or lips and is lopsided and slightly open and it's very sensitive. Before, it was just a normal looking slit. I've switched to wearing briefs when walking around which prevents my penis from moving around too much and lessens the irritation. I switch to boxers when I'm at home because I find them to be more comfortable. I've found that these measures help, but it's been 3 months now and I still continue with a funky looking overly sensitive meatus. Don't know what to do since all the doctors tell me it looks normal.