Spit up

My son is 8 months and I nurse him he eats solids and table food. I do give him water (baby kind) but only a couple oz especially when it really hot but lately he’s been spitting up and he’s never done it as a newborn. It’s a everyday day thing he drinks milk then he’s spitting it up some times it’s small but mostly it’s like big chunks. I assumed because it’s hot but even only chilly days or days we sit in the ac in the house he’s doing it! Any one have an idea?