baby gagging

Hi mommies. I don't know if I should be concerned. My son is 8.5 mths old. Eating solids and doesn't drink his formula from a bottle anymore bc one day he just decided he didn't want it anymore.. Not even in a sippy cup so he only has formula when we mix it in with his rice cereal and oatmeal. He loves water so drinks lots of it. He was gagging or vomiting a lot for about a wk (last month) I already went to the pediatrician and he's fine. Gained normal/great weight and length. So she says she guesses as long as he's healthy, gaining weight and hydrated then he should be fine.. But this wk he's gagging again and vomiting occasionally. Every time we feed him his foods. Is this normal?? He's still his usual self.. Alwahs Happy.. Smiling.. Etc. Please help.