Do you leave crickets in his cage? I did this with my bearded dragon and the crickets would chew in his lips at night looking for water. It was always more gross when he woke up.
Poor guy, looks pretty uncomfortable. Can't imagine he is able to eat very well. Do you have a good vet? As already stated, I think your best option is to get him to one ASAP before it gets any worse or causes secondary infection.
You need to get him to a vet asap. The areas should be cleaned out properly. Chameleon "pus" is like cottage cheese. It won't heal if its not cleaned out. There should be a culture and sensitivity test done to determine what bacteria is involved and what antibiotic will work the best at getting rid of it. Mouth rot is often stubborn so it needs aggressive treatment.