Rodent ulcer? Feline acne? Bleeding today.. worried.

I've never dealt with rodent ulcers before and have minimal experience with feline acne. I noticed a bump on my 14 year old's lip Friday night. It's on the right side which is the side where he has an ear that bothers him and had one tooth extracted recently. He does a fair amount of rubbing on that side of his face, rolls around on concrete/grass outside, and scent-marks(for navigation, he's blind) so the possibilities of what he might have come in contact with are endless.

This afternoon we were in the back yard with the cats and I noticed he was bleeding. I cleaned the wound with peroxide and warm water before applying colloidal silver, then called his vet. Unfortunately, his vet is out of town until August so I asked to have one of the other vets call me back. He's been through quite a lot recently(heart block under anesthesia, etc) so I'm not in a hurry to put him through the stress of yet another vet appointment. The vet whom I spoke to and poorly described the situation to(experiencing a great deal of brain fog right now) agreed that I should just keep an eye on it.

Any advice for what to do for him or what it could be? My current plan is to continue giving him his supplements(for immune support/heart health/etc) and to apply colloidal silver here and there. Any other tips would be great. It's such a bad location for him but he doesn't seem bothered by it at all. This is the cat who didn't seem to be bothered by being partially paralyzed, having a scratched cornea, and the list goes on, though.  

I've attached some pictures that I took Saturday as well as today(after I saw the bleeding/cleaned the area).  I'm going to attempt to get a better, closer picture when he wakes up later.

Saturday:

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Today:

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First off I'm so sorry to hear of all the troubles your little guy has been having! It sounds like he has been through the health ringer lately. 

I honestly don't know anything about rodent ulcers or even feline acne. I just wanted to offer some support to you. I know it can't be easy dealing with one health crisis after another and I understand your reservation about putting him through the stress of yet another vet visit. I think at some point it should be checked out just to be sure it's nothing serious, but if the vet told you to just keep an eye on it then I would do just that and continue with his regular health maintenance. Hopefully it will remain un-bothersome but if that changes It's clear from everything else you have done that you will take him in. Remember that cats are experts at hiding pain (and clearly your guy goes above and beyond) so watch carefully for any changes to his behavior and routine as that may be the only way he indicates to you that it's hurting him. I would think given the location so close to the mouth that it may effect his eating so keep a close eye on that. 

Hopefully someone else will come along who is more knowledgeable on the subject and who may be able to advise things you can try to make him more comfortable. I just wanted to send vibes that it doesn't get worse and let you know that we are here for your emotional support as well as his physical well being. Feel free to vent if you need to! 

I have no experience with rodent ulcers, but it kinda looks like a bite of some kind.
 

Did you ever figure out what it was?