9 month old continued eating problems

R
I don't know what to do at this point. At 6,7,8 and now 9 mines old, my son is still having problems with eating. He's always gagging here and there no matter what it is and anytime I've given him anything other than his baby crackers and puréed foods, he will throw up. All he has to do is slightly gag once and it all comes back up. I waited awhile since the last time thinking he might be ready since he's been doing good with chewing his crackers but nope. I gave him a couple small slices of avocado today which he really seemed to like. The first slice went down ok but on the second, he just puked it all up. It happened so fast idk if it was from a gag or his stomach just rejected it?? If it was from gagging, it was barely at all. I'm just getting so discouraged. Why does this keep happening? His 9 month checkup is tomorrow and in hoping there is someone who can help me with this. He wanted the avocado, even got mad after I had to take it away ☹️ Any other moms have a child that's been this way? Anything I can do to help with this??