Formula problems? Gas & constipation

My baby, who will 4 months on Oct 8, has been on enfimil gentlease since about 3w old. Two weeks ago I tired to switch her to the parents choice brand of gentle. She started to get super gassy, super fussy, started waking up in the night when she has been doing 7-8 hour stretches and she started to not poop everyday and have thicker poops...so I switched her back to enfimil after only 4 days.....this was 2 weeks ago and all these problems are still going on!!! She's constantly whining in pain....is always pushing to pass gas and try to poop. 😢

She's been on gas drops and probiodics for over a month too. I gave her mommy's bliss constipation ease ( not even 1/2 the recommended dose since its 6 month plus) a few times and she will poop but the constipation keeps coming back....its not like a one time thing . we are going to the docs this afternoon.

Does it sound like it could be a formula problem?? But she's been on the same formula since 3w olds (minus those 4 days)