Should we switch formula?

Hi ladies, I’m turning to you for help because I’m confused!

My son is 2 1/2 months old and he’s currently on Similac Pro-Sensitive. He started out on pro-advance when he was born, but he seemed like he was in so much pain during and after eating, and he was spitting up a lot.

When he was a month or month and a half, I switched him to pro sensitive. The pediatrician said I’m welcome to switch his formula based on my instincts since he’s gaining the appropriate amount of weight.

I made the mistake of buying the Walmart sensitive formula brand and he started spitting up a lot again. He was on that for about 2 weeks before I switched him back to pro-sensitive. He has been on pro-sensitive again for about 4 days now and he’s spitting up a lot again, and he seems to be in pain again while eating or after he eats. He’s extremely fussy. I feel so bad for him and I don’t know how to help him.

Does this sound like a milk protein sensitivity? Does it sound like an allergy? Or should I give it more time to see if his body adjusts? I’m not sure if I should switch again, to something like Similac Pro-Total Comfort or Alimentum?

I apologize for jumping around in the timeline. If you have any advice, suggestions, recommendations, or experiences, please share! Thanks in advance for your responses!

Here’s my little guy. 💙