spitting up milk

hi mummies, my baby is turning 6 months in about 2 weeks time. up till date, he is still constantly spitting up milk. he is a fully formula fed baby, and this happens even during my breastfeeding days back then. it does not only happen right after feeding time, but throughout the day. we’ve tried burping him, sitting him up after each feed, and even changed formula twice. still no difference. went to the doctor and was told to reduce his milk volume. done that already and still no changes. initially thought it will go away after the first few months but starting to get worried now.. any advice mummies? should i change formula again?