Keep going with the courses of antibiotics.
When I had an infected ankle the first course of antibiotics didn't make a lot of difference, so the doc prescribed a second one. That made things a little better but still not completely right. When he prescribed the third course , the doc said "It's not at all unusual for lower limb infections to need multiple courses of antibiotics. This third one might do the job but don't be surprised if it actually takes five or even more" (I was lucky in that the third one did the trick but you might need to keep going longer).
You could also try taking supplements that have natural antibiotic properties, such as garlic.