Personally I won't be giving him any antibiotics but if you think he really needs it then, you may want to try a water soluble like oxylet. Baytril is good but I would be afraid the doses is to strong no matter how little of a size you give him.. I would be Leary on giving him it. Is he walking is he holding his head up what exactly is he doing and not doing.. I can check with my vet to see what the dose is but he may suggest something else that's not so strong exspecially at just a young age..
