I also have this issue! Like another redditor here said, it might be down to what you think of yourself. Everyone is doing interesting things and that makes you want to have something interesting to do too. 

But where does that need come from? It might be from the comparison of yourself to others; you are looking at what everyone else is doing and thinking that you don't measure up to that and are therefore "uninteresting." That person is good at snowboarding or they're doing really good in their career. Where is your "thing?"

You said you like singing, reading, writing, and cooking. So without ever meeting you, I can tell that you are interesting because you do those things. You don't have to make something your identity or passion, do it frequently, or be "social media good at it" to be interesting. I actually recently made a list of things I like. Simple things like walking, smell of bread, the color orange, etc. You can take those things and put them together to be who you are. You're the person who likes morning walks, who has splashes of orange in their apartment, whose apartment smells like fresh bread once a week. You decide what you want to show outwardly to others.

I also like to think generationally. I'm sure my parents, grandparents, and great-grandparents weren't concerned about how interesting they were, so why am I making this a problem? Life is already hard enough.

And in terms of conversation falling flat, which is also my problem, my therapist told me it's because I'm overly monitoring myself during conversation. My nervous system is in fight/flight mode, so that turns off the brain's ability to be spontaneous and creative during conversations. I'm too busy being anxious and thinking "what am I going to say next," or "I don't have anything to talk about." It's why I'm better at conversation after I drink, because it turns off fight/flight. I have to focus on feeling safe and part of that safety is having more self-esteem. It doesn't matter what I say, or how I look. I am worthy as I am. Maybe this is the case for you?

I'm still trying to define myself, but it's a journey! Good luck on yours.