Hey Snake Girl! I have just recently obtained a rescue/adoption with the exact same problem. I am going to tell you what my vet told me! I am not an expert in any way I am just going to relay that info to you.
First of all ...switch to overhead heat..get a lamp or ceramic emiter. The heat on the belly is not good, it is uncomfortable and the snake will have problem regulating. The heat also breeds bacteria.
I change the substrate twice a day or as needed. I use paper towel, I was recomender this or newpaper ....without print!
I soak him in a warm betadine solution watered down to the color of week tea. Once a day for about 10min. After which I blot and dab the infected area with clean paper towel. The odd scale does come off. I purchased the betadine from the local drugstore for $13.00 Canadian per 1 ltr. I do this in the morning.
At night I apply a liberal amount of polysporin. Ever morning I wake up and change the substrate because it will seep out and leave the paper covered in a greenish puss.
I have been keeping everthing as clean as possible to provent any further infection. Like The Omen said fresh water and a clean bowl.
In a nutshell I have followed this regime without fail. So far so good, this seems to be working even though it has only been a week. I am going to be following this thread because I am learning along with you and hopefully we both get a couple of very healthy snakes from this
btw you are right about leaving a pet with a freind! The guy that I adopted this ball python from did the same thing.
This was taken after a good cleaning in the first couple of days