Had 3 remicade (infliximab) infusions for uc so far. feel very tired most of the day and can't eat well due to nausea. is it due to remicade (infliximab) side effects?

Probably not: Most of the side effects of Remicade (infliximab) are felt during the 2-3 hour infusion. More likely you are tired because you are anemic. The nausea may be more due to your uc.

Possibly: Remicade (infliximab) is a potent medication and certainly capable of producing those side effects. See http://www.Ncbi.Nlm.Nih.Gov/pubmedhealth/pmh0000267/.