Oh, Smithy hun It's awful when your baby is screaming in pain hun. I don't know much about formula but I was going to suggest sugar water, just until she does a poo. You can put about a half teaspoon of brown sugar dissolved in about 4oz of water. I've never done this myself, but I have been told that it can help.

Can you change back to the other formula she was on? Thickened formula can definitely cause or worsen constipation and maybe that's what has happened. It may mean that Charlie goes back to 2-3 hours feeds, but hopefully she won't be constipated and distressed

If it doesn't improve definitely see your GP hun and they might be able to give her something.