Help what can it be?

Baby is 4 weeks today and we have his 1 month on Friday

He seems to be in aoinw hen he eats of the breast and the bottle we supplement with formula and nurse of demand he never gets a bottle before the breast. I give him gas drops on occasions because he wasn’t responsive to burping. Right now he’s asleep but kind of yelped a couple times. He will also arch his back when nursing and then unpatch and cry. I’ve been trying to keep him upright after feedings in case it’s reflux but. Just wondered if anyone had similar.