Yikes. Looks similar to a issue one of my big females had a few months ago: found out she was rubbing herself in her tub and inflaming her upper lip and causing it to swell up (might have broke a tooth too but we were never sure: everything cleared up). Here's some pics for you to compare:







I had to take her to the vet who recommended twice daily diluted Betadine swabs to the area (ie inside the mouth along the tooth line on that swollen side) and warm compresses to the side twice daily as well (exterior compresses). She also got three shots of Baytril to fight any infection (looked like she broke a tooth off possibly). She cleared up and even after she re-swollen herself up a few weeks after her vet visits it cleared within a few days of the same swobbing and compressing. She's now perfectly fine and feeding great on live rats after going off feed during treatment.

I would recommend finding a good vet (even if you need to barrow someone's car to get there) because your snake really needs to see someone knowledgeable and herp vet certified IMO. How does the inside of his mouth look? Anything cheesy in there?