Why won't he sleep??

So my little boy has always had trouble sleeping - at first he just wanted to be held, then he would go down in his crib but I had to put him on his side because he had so much wind. We then found out he had tongue tie so since that's been sorted I thought it would get better, if anything its worse! He is now just over 4 months, he follows a bed time routine, same time every night and takes about 15mins to finally nod off if I put him down drowsy. But he wakes up screaming! Sometimes 20mins sometimes an hour. I thought it was reflux, so I've been given gaviscon to put in 4oz of expressed milk - thats not going to happen as it would take me all day to express that amount, so I put it in formula. He can wake up between 3-5 times a night. And then he sometimes only naps 20mins at a time during the day!! I watch for his cues, give him dummy and rock him but sometimes I give up after half hour cz he won't go to sleep and I think maybe I mid read his cues, for him to be screaming the house down 10mins later. He nods off in the car, but wakes up as soon as I stop, and will nod off in the pram but can snap awake after 20mins or sleep for longer! Anyone else struggle with this?? Any tips greatly appreciated!