1-2 days after I started experiencing a slight discomfort at the tip of my penis (meatus?). This discomfort last for about 2 weeks where I could notice it constantly rubbing on my underwear. No burning when peeing or discharge though. Then after about a week or so of not noticing the irritation, it came back. I also think there is a slight swelling at the tip of my penis, but can't say for sure. It also feels noticeable after I masturbate. Still no burning or discharge. 

1 week after the exposure I started to get a slightly sore throat and feel like a cold was coming on. It never turned into other cold symptoms, but the feeling was constant and went away about 1 week later. Then I had a burning sensation on the tip of my tongue that only last a few days.

I did a urine test at 2 weeks for chlamydia, gonnorhea, mycoplasma, trich, Haemophilus ducreyi, and treponema pallidum. All negative. 

Then at 4 weeks did a standard blood and urine test. All negative. Also did a mouth swab for gonnorhea and chlamydia. All negative. 

Now 5 weeks later I developed a sore throat again along with congestion. 

1. With all the negative tests, is there a possibility of some other STI that I haven't tested for?

2. Is there a chance I can pass whatever I have to someone else of I engage on oral sex again? 

3. Should I test one more time for syphilis at 6 weeks for a conclusive test? 

Your symptoms have not been typical for any STI, but they were suggestive enough to warrant testing, exactly as you have done. But all the negative tests are reliable. With those results, the most likely explanation for your symptoms is psychological -- i.e. anxiety increasing your awareness or sensitivity to minor symptoms or even normal body sensations that otherwise would not be bothersome and maybe not even noticed.  As for the specific tests you had, some were unnecessary. Trichomonas is strictly a heterosexually transmitted infection, no risk at all from oral sex or sex with men. H. ducreyi and the genital mycoplasmas (i.e. M. hominis, Ureaplasma species) are entirely normal in the genital tract and even positive results do not require treatment.

Those comments pretty much answer your numbered questions, but to be explicit:

1. There is no realistic chance of these or any other STI.

2. And therefore, it is clear you have nothing you can transmit to another partner by oral sex or any other kind of sexual contact.

3. It is true that it takes up to 6 weeks for conclusive syphilis testing. However, based on your symptoms (and lack of typical syphilis symptoms), the chance you have it it is near zero. But feel free to test again at 6 weeks if you'll sleep better knowing the negative result.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

If there is a slight swelling of the meatus or a split urine stream when I first start going, would that be a troublesome sign? Sometimes when I notice the irritation a lot, I spread the tip open a bit and it looks like just on the bottom of the lip there is a slight red scratch almost (very tiny). Would this be indicative of anything either? 

Thank you again. 

That said, if split stream or apparent meatal swelling continue, evaluation for a non-STD urinary tract infection might be a good idea. Although oral sex isn't a likely origin of such an infection, it could happen.

As this is my last reply, I wanted to thank you for your help and advice!

Thanks for the thanks; I hope the discussion has been helpful. Best wishes and stay safe.