It's unlikely a primary herpes outbreak because those take longer to happen after the initial infection. If it's HSV at all, then it's the dormant virus coming to life after your immune system was weakened. However, I'm still skeptical that this is viral.
When I used to rave and do MDMA often, I would sometimes get swollen lips from rubbing them together all night. It's something unconscious that you might not have even been aware of doing. I never chewed my lips but the constant rubbing and lip smacking made them incredibly irritated. Sometimes using chapstick helped but on the worst nights I would still have swollen lips with sores the next morning.
You can apply a dab of salt directly to the sore. It will sting, but then feel better. Rinse it off after that. Keep your lips conditioned with chapstick.
The swelling should go down soon.