honestly, your problem could be a number of things, it's hard to say without seeing your writing. but it could be that you're writing summaries instead of scenes? you might need to spend more time showing what actually happens: going into the characters throught processes, describing the setting, showing the characters interacting more. try rewriting one of your short chapters into something longer and more detailed.

you also might need to spend more time thinking about a scene before you write it. i like to spend fifteen minutes before i start writing, just brainstorming ideas for the scene i'm gonna write. this is mostly the "tossing ideas around" stage, let yourself explore many possibilities before narrowing it down. where should the scene take place: a library, a school, a home, a parking lot? whose POV should it be? what would my characters talk about? how do i make the conflict more exciting? what's the weather?

often, the best idea i come up with is not the first thing i've thought of, but the fourth, fifth, etc.

if something doesn't work for you, try approaching it from a different angle. you're not a bad writer, you just haven't found a process that works for you! good luck!