How do I (25M) make my girlfriend (25F) happy?

I've been with this girl for about a year and a half. Everything else between us is fine but I feel like I'm missing out on something because she never told me what she likes and what she doesn't like. I've tried asking her multiple times but she's too shy to tell me. Everytime I'm doing something she just says "it's fine". I'm getting frustrated because I want to make her happy but I don't know how and she won't tell me. I don't know what to do. I've tried doing random things, buying random stuff, giving random hugs and kisses. But nothing seems to be working. I'm ready to break down.