Tummy Issues

My daughter started out on Similac Pro-Advance and at about 3 weeks old we changed her to Similac Pro-Sensitive because she was so gassy and fussy all the time and was really struggling. When we first started her on the sensitive things were going well, but in the past few days we’ve gone backwards again. She is also REALLY struggling to poop. My next move would be the Similac Total Comfort. Is anyone using the TC or having a similar experience? I just hate seeing her so uncomfortable 😫