Have you been to a health care provider for examination? I cannot tell what you might have, from your description. However, the combination of lymph node enlargement in the groin plus a skin rash of trunk raises the possibility of syphilis. It does not sound at all like any other STD such as HIV or herpes. Conceivably scabies if the rash on your trunk and waist is itchy. Most likely, however, it is entirely unrealted to the sexual encounter you describe.
But the bottom line remains the same: See a health care provider right away for proper evaluation and diagnosis. If cost or confidentiality is an issue, or if you aren't confident your own provider's knowledge about STDs, visit your local health department STD clinic. But don't worry all about HIV; there is no chance that explains your symptoms.
Please no follow-up questions here with more detail about your symptoms. No matter what you say, my answer will be the same: I will not be able to tell and you will have to see a health care provider.
Happy new year-- HHH, MD
The only way to be 100% sure is to get a test. You're likely OK, but get tested after 4 or so weeks if you want to be sure.
Good luck, Happy New Year!
HHH, MD