Help :(

In need of help. Had my daughter 5 days ago. I been breast feeding her. Started using some soy enfamil on her probably 2 oz only since 2 days ago. She has been gassy and has been having trouble pooping. I can see it on her expression. Also everytime I pump and give her my milk sometimes I mix the fresh one with the one that has been on the fridge. Is that bad ?

Also should breast milk be refrigerated at all times. Sorry Im a first time mom and Im so freaked out about my little one.