I wouldn't feel bad that you do not know how to treat your sick turtle. While plenty of people in this forum have knowledge and experience on the topic, your veterinarian is the only person qualified to tell you what is wrong and how to treat it. You are on the right track by optimizing husbandry. With sick tort's raise the total ambient temperature just a few degrees to help produce a fever.
See your vet in the next day or two and he/she will most likely take a sample of exudate to find out what bacteria is causing all the problems, and what antibiotic it is most susceptable too.

Ian