The first thing you needs to do is to eliminate the infection. It sounds like your son is still infected, because once you change the antibiotics to Amoxicillin then the antibodies increases and causes the changes in his behavior.

The 4 different cases of strep throat he had back in Oct/Nov may not be 4 seperate cases. It could be that the antibiotic from the first strep throat did not eliminate all the bacteria that caused the infection. So it came back over and over again. A few courses of antibiotics could cause bacterial resistance. If his infection is persistent, does he need to see an infectious disease specialist?

Did the doctor do a throat culture? Can he run an antibiotic susceptibility test to see which antibiotics is the best to fight this infection? Is it possible that the bacteria is resistant to antibiotics, or maybe the bacteria is resistant to just that type of antibiotics?

There is also something called plasma exchange or IVIG to filter out the antibodies. However, the infection has to be eliminated first. See this article: http://www.childadvocate.net/PANDAS_treatment.htm

Good luck!

Cindi