Constipated and gassy baby :(

My LO is 2wo and she's been constipated and gassy for about 4 days now. I breast feed for about 30-40 mins and I give her about 1oz of formula every 4 hours. She was on regular enfamil but our Doctor changed her to enfamil gentlese 3 days ago. So far there has been little change, I hate seeing her suffer and get all red every time she passes gas or poops. Any tips?