How often have you been feeding him after you noticed the impaction??
I am surprised that the vet didn't provide an antibiotic to at least try to help.
I tried a dose of Repta Boost soon after I noticed the impaction. He wasn't eating a day or two before. Then another dose of Repta Boost a few days later, then a small piece of worm two days ago as I thought that may help loosen it. That's all he's had.