Many people have a quick response to remicade. My son's first treatment took about 3 days for obvious improvement. But other people don't see improvement until after the first 3 loading doses.
I think it's normal to feel tired - especially if they premedicated you with benadryl which is standard practice. The sore throat - my son hasn't ever had that. Maybe the clinic air was dryer than you are used to or you are a little dehydrated?
Hope you feel fabulous soon.