I’m worried I might have caught something like Gonorrhea, Syphilis, or Chlymydia, but I’m not sure if I’m just anxious and manifesting symptoms. I keep feeling my lymph nodes and I think I can feel my groin ones but I’m also a slim build so not sure if this is normal (5.5” ~130lbs). I think I had a canker sore two weeks ago but healed within a week (and also hurt). Sometimes I find dry patches on my testicles, but I’ve had this issue even before this sex encounter too. 

What are the chances I caught an STD from this encounter? Is it low enough where I can just move on and forget about this?

You describe a near zero risk exposure for any and all STIs, because of the details of the exposure itself; the low risk your partner is infected (most people are accurate in their self assessment and rarely lie about it); and doxy-PEP. Actually, the exposure did not meet standard criteria to recommend doxy-PEP because the risk of syphilis or chlmaydia was too low:  it's officially recommended only after unprotected anal sex. In any case there is no realistic possibility you have gonorrhea, chlamydia, syphilis, HIV or anything else. The symptoms you mention don't hint at any of these -- and anyone can feel lumps in their groin if they try hard enough; this isn't abnormal.

I advise no testing of any kind and if you have a regular partner, you can safely continue your usual sexual practices without putting them at risk for anything.

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

HHH, MD