I was like that when I was living in an environment that caused depression & anxiety. I had no idea that wasn't me until I escaped that environment when the "me" that had been hiding inside if me for 54 years was finally free to come out.
We don't know if that personality is us or our environment. I look back & sensed that I wanted more....but even now I limit my socializing because I get exhausted....though I enjoy chatting with people when I go to a store. I moved from Los angeles to a little town of 8000. I feel more comfortable in small groups,towns, etc. Just feels more manageable & comfortable & that helped me very much.
Saying all this.....however it still could just be the way you are.....& that needs to be ok if it is.