medication inquiry

I have a 7mo old lab/border collie. At his last visit he was given a distemper + Corona shot and a rabies shot. He was also given a shot of medicine for skin infection plus tms 480mg to take home. The only information that I was told was to give him 1/2 of a pill every 12 hrs. I have given him 1/2 of a pill every 12 hrs since last friday. He is not acting like himself at all. Could there be a problem? If there is a problem what can I do to help him out of this?

Do one of these 2 things:
   
1) Telephone the vet's office & get the fax number. Write up a full description of the dog, its treatment, condition & behavior. Call the vet, tell them you'll be faxing the letter to them, so they check the fax machine immediately. Fax the letter to the vet with a number for them to call you.
   
OR
   
2) Telephone the vet & describe in detail what your concerns are. Ask for a call-back with advice on what to do, & should the dog come in to be looked at again?
   
Either way is a good way to approach the problem.