liquid formula and diarrhea?

Anyone used liquid concentrated formula and had issues with diarrhea? My son is 5 weeks old. I breastfed for 3-4 weeks. So hes ben in formula for maybe 1 and a half week. First was soy presobee concentrate for two days then we moved to infant concentrate (yellow enfamil can) but hes ben havinf runny green poops nothing any kind if peanut buttery consistency as i have read!