Diarrhoea: do i panic now?

My baby had a vaccination, then a fall and was discharged from KKH recently after the fever and vomiting subsided. So all was good. But once at home her appetite dropped and there was mucus in her pooo. The colour changed from the usual breastfeeding mustard yellow to watery yellow and light green! Now she's sleeping more than usual and occasionally throws up. Is this a stomach flu? Or remnants of a vaccination? Do i go back to the hospital or just peads clinic? Help...