Kitten with sore on his neck

I have a 10 week old kitten that has a sore on his neck. At first we thought maybe his brother was playing with him too rough but it's not getting any better. I've cleaned it with peroxide and put an ointment on it but I'm completely clueless on what is going on with him. We have 2 cats (the mom and dad) and the two kittens but he's the only one with this. Does anyone have any ideas on what this could be?

It looks like it may be an abscess.  Has there been any drainage from it?   It would actually be better to use warm soapy water rather than the peroxide.  I don't remember all the specifics but just plain water would be better.  I would take him to the vet to find out what it is.