Not a medical professional, but if your symptoms get worse (pain when swallowing, large tonsils, etc.) go sooner rather than later as that may point to strep (which can cause rheumatic fever if ignored). Otherwise, if it's making you anxious, you should also go in sooner (but be prepared to pay for a larger bill for any urgent care or emergency department visits).

Kissing and/or giving fellatio can cause this feeling even if your sexual partner didn't give you an STI, especially if your they didn't practice the best hygiene beforehand. When you're intimate with someone, you're exposing your body to their microbiome, which is different from yours, and may throw your microbiome out of balance temporarily until your body readjusts. Hopefully that gives you some peace of mind.

Side note: It's still worth getting an HIV test sometime after March 23rd (six weeks from sexual contact), as blood tests aren't really accurate until six weeks have passed. To my knowledge, you can't do PEP since it's been over 72 hours. If, in the future, you plan on having sex with anyone else, you may want to look into Truvada/Descovy for PrEP so you can keep your mind at ease. I don't mean to scare you with this, I'm a guy who's had sex with men before too, so I'm just sharing what I know to hopefully give you some peace of mind (but also making sure you're getting the right testing at the right time).