Formula help

Li

Hey Moms. I am very upset that due to a need to take medication that is not safe while breastfeeding I have to switch to formula. My 4 month old has been EBF up until then. Her ped suggested and gave samples of Gerber Gentle. She has taken to it fine and also gets 4oz breastmilk a day from my frozen stash. However, she has had TERRIBLE smelling gas and poops. Today she had 5 dirty diapers that were sticky and dark green. Then had one unlike one I have ever seen. It resembled cooked scrambled eggs :/? I am thinking of changing formula. Can anyone suggest a good brand that is closest you can get to breastmilk. It really kills me that I have to stop breastfeeding and want a formula that is the next best thing. PLEASE HELP!