It is odd that your pdoc doesn't have back-up at all. Anyway, one other option would be to call a 24 hour pharmacy for a med question. A pharmacist could answer basic, general questions about a med if there was a problem or side effect you are wondering about. Mind you, their advice might very well be call your doctor, but they would at least let you know if this was an emergent situation or something that could wait.

My pdoc is in a large practice and I can always get hold of some pdoc (not always necessarily my own) in an emergency, but they don't consider med questions emergencies and probably wouldn't forward that kind of message.