My son was seen by a doctor on sunday for a respiratory tract infection and prescribed antibiotics. he seems to be getting worse, should i take him back to the dr who is not my regular doctor, or give it more time.

Missing info : We can provide a better response when you provide info like the age, present activity limitations and what/why an antibiotic was given. If the kid is refusing fluids or not active/playing it is worrisome. If your regular doc is not available a recheck by the treating doc may be worthwhile.

Seek a re-evaluation: When in doubt, always feel comfortable seeking a re-evaluation. If it has been several days on treatment and things aren't improving or actually getting worse, a re-evaluation is quite reasonable.