Cat with Bartonella?

5 weeks ago i adopted an amazing, beautiful little 7-12 mo, sickly boy from a shelter. he was sniffly, boogery (often bloody), labored breathing, loose stools, skinny, halatosis, gingivitis, and then some. regardless of his maladies, we fell in love (his sweetness factor is 11) and now i am nursing him back. after a useless round of clavamox, the vet opted to test for bartonella, sure enough it was positive. during the 7 days waiting for the results, the fab kitty i adopted seemed to have disappeared, he was lethargic, crabby and prefers solitude. i am now on day 13 out of 21 with zithromax. after 7 days i thought we had turned a corner, he was his sweet self again, with lots of purrs, talking and cuddling. now, the past 2 days he seems to have regressed again. has anyone else experienced a similar set of cirstances? can anyone share an experience with bartonella?