preemie formula changes please help!

Ok my son was born at 35 weeks and couldn't latch so I have been pumping and bottle feeding it to him. I had a huge supply and within the first month of his life I had already pumped enough to supply him for 6 months.... He also had issues gaining weight and his Drs put him on Neosure formula 3 times a day... He eats every 4 hours on the dot, usually 3-4 oz at a time and typically takes about 30 minutes to eat.... he is now 6 weeks old and doing well..... I will be going back to work this week and I am blessed to be able to just take him along with me, however with my line of work I am on the go all the time. I don't have access to a bottle warmer, I have stopped pumping and I'm almost dried up as I can't continue it with my job, it would just be too much.... so being able to stop at a restaurant to get a cup of warm water and mixing up his formula while we are out will be perfect, those 3 formula meals will just take place during the day time and it will all work out... my question is, should I switch his formula? the neosure makes him sooo gassy and constipated and I hate how it makes him feel. that reason alone makes me want to switch but his pediatrician wants him on the neosure. eventually my breastmilk supply will run out and we will have to switch to full time formula anyways so I want an easy transition at that point, if he only needs the extra calories in the neosure 3 times a day then would him getting it 6 times a day be too much? I wouldn't really use 2 different formulas right? is there another high calorie formula that's easier on their belly that I could feed 6 times a day? does he even need the extra calories if he has caught up weight wise? I stood in the formula aisle reading cans for an hour today and just got overwhelmed... I am planning to change his pediatrician after his 2 month shots as I don't like his thoughts on how much my baby should be eatting (he said 2oz every 4 hours at 1 month old 🤤 that's not nearly enough) so im not sure if I trust his opinion on the formula thing anyways.... the dr we got is great with preemie babies but my son is pretty much caught up developmentally, he is just little for his actual age. I have already seen another Dr and so long as my little guy doesn't have any preemie related issues with his 2 month shots and is caught up weight wise (I have no doubt he will be) I will switch drs.... what would you guys do with the formula situation???