Baby Spitting

So today I've noticed that my baby has been spitting a little bit almost every feeding. He used to spit a lot more (almost like projectile vomiting) but we realized the nipple.flow was too fast on the previous bottle we used.

Fast fwd.. we are now using Dr. Brown's anti colic bottles which has help with his gassiness a lot. He still needs burped usually every ounce he gets but he does not burp as loud as he used to (it was like an old man). We also switched from Similac Pro-Advance to Similac Pro-Sensitive and it's been 5 days since we made the switch and again, we notice less gassiness.

He is getting 3 oz (2 oz breastmilk + 1oz formula) (I have low supply and can only get 2oz) Nothing else has been new since 5 days ago but now he is back to spitting up again--some just look like milk curd but sometimes it's a little puddle of milk once he is sleeping.

He takes about 15-20 mins when he feeds and gets burped often. He is positioned upright when fed. I want to know if it is something I'm doing wrong? What could cause this? I know some spitting is normal but it has really been bothering me since he stopped doing this for like 2 weeks and now we are back.

Could it be something I ate that is making him spit up? What else can I do? Thanks!