Aptamil pepti making baby worse..

My son is 3 months old. Since he was born he has suffered with reflux and also really bad trapped wind and gas. He also was only pooing once every 4 days. He seems like he has a constant tummy ache and in pain. He cries, draws his legs up, arches his back etc. He has also had a cough and been congested since birth. We tried gaviscon and carobel both of which made him extremely constipated and even more uncomfortable. The gaviscon didn’t work anyway. The carobel worked a bit but made him even more gassy! I decided to go down CMPA route just to rule it out. I took him to the GP who was adament that’s it’s not CMPA because he doesn’t have mucous or blood in his poo. She said it’s just reflux. I said I wanted to try allergy formula anyway just to be sure. She eventually agreed and prescribed us aptamil pepti. He has been on this formula for 4 days now and seems to be in agony on it! He is farting more and I also think it’s making his reflux worse. I knew there was a strong possibility that his reflux would get worse but I wanted to try everything before going down the omeprazole route! Now I don’t know what to do! Do I persevere or should I stop pepti? Is there a chance this is just his body getting used to the new formula?