Formula feeding

I am trying to switch to full formula, but doing it slowly. My son gets a bottle at least 3-4 times a day. Usually does 3-4 ounces, mostly 4 ounces. I find that he is spitting up a lot, and it’s not forceful, but he burps and it comes out. I know that most people say spit up looks like a lot more than it actually is… but there is never a feeding where he doesn’t spit up… and it can be multiple times, or an hour or two later… I’m wondering if it’s the formula.. and thinking maybe I should be switching. Has anyone experienced this… and did a certain formula work better? First i used Kendamil and now Aptamil. Thanks!