I think I have a stomach virus and I am scheduled for a blood test tomorrow morning (fasting lipid panel, CMP w/EGFR, CPK, PSA). Should I postpone?

Should not impact. The tests you listed are not likely to change if not feeling well. Consider the phlebotomist, though and postpone if actively symptomatic so you don't transmit it.
No need to postpone. it should not make a difference in those tests,Some viral inf can decrease WBC (white cells) count.