Before I started living stealth (16) I was always an out going 'tomboy', class clown, your average center of attention fool. When I started at a new school where NO ONE new anything, besides the principal and my social worker, all of a sudden I felt pushed into this shell. I made a couple good friends, but definitely didn't want to be the spot light anymore.
Looking back - it was because I knew the more attention I had on me, the bigger chance someone would say something, or figure it out. And I didn't want that. I could finally be at ease without people talking sh&% and for years I held back my true 'self' because of it.
I didn't start T until a little under 3 years ago, I'm 27 now, and remember when I did start, feelin the same as you. I honestly think a lot of it is the initial changes T can do to you. Everyone reacts different to it, but I definitely clammed up. I didn't want to go out and have fun, I was much more "happy" sitting at home, alone, screwing around on the internetz. I remember a couple times, friends would come over, KNOWING I was at my apt, buzz my apt, throw sht at my windows, and I'd turn off my lights and pretend I wasn't there just so I didn't have to go out and face the world.
As hard as it is, I think it's better sometimes to just force yourself out there. There were numerous times I'd go out just to shut some people up, and I always ended up having a good time, and would be thankful I decided to go out in the end.
Now 3 years into my own journey, I've become a lot more comfortable in my own skin, and have slowly started getting back to the old jackass me. Lonliness is a dreadful feeling man, and as cliche as it sounds, you gotta live in the now, knowing you're not promised tomorrow. Try to brave it out, and explore a little.