I agree, go for the second opinion. I had one that lingered on for the better part of three months - it took repeated doses of a variety of antibiotics, and several days in hospital on IV antibiotics, to get on top of. They should have taken several swabs by now to check that the bacteria is actually responding to the ABs you're on. They should also do another ultrasound to check where exactly the "collection" is.

Re the betadine - you've mentioned the gory details so I'm assuming your wound is still open in parts and discharging? I was told not to use anything on it until the wound closed. Once it was closed I used the spray-on betadine for several weeks, and it was great. While it was still open, I would bathe the area every day with STERILE saline solution (swab it on with cotton wool balls) and then hairdryer-it dry, which seemed to help.