Why do I feel tried after being in public?

I think the best way to put it is that its draining for me. Say when I go to works for the six hours I am there its OK. By the time I get home I just want to sit in my room and not be bothered by anybody until tomorrow. Even by the end of my shift at work I can barely talk, mouth is completely dry (even after drinking recently), and I feel like my face is permanently in a tired state. Can't even fake smile or nothing, I end up just nodding/ waving and leaving. Its not even like I talk a lot on the job (I work in retail), in fact more times then not I am just stocking shelves and stuff all by myself the entire day. I rarely if ever stop to chit chat with other employees. Not because they're bad people, but because one I can't do that and two I don't want to. I don't mind to much talking with customers however, not sure why its different with other people.

At times I feel like I am Dexter Morgan from Season 1 where he was kind of like an outsider, and was never able to fit in anywhere. Let alone be emotionally invested in other people. Without all the homicidal tendencies of course.

Another way to explain how I feel is that to me being in the presence of other people is like I am on stage in a broadway theater. Like there is so much pressure and everything I do or say must be on point or I'll be embarrassed and thrown off the stage. Once I get home I just relax by myself and its really the only time of the day where I am happy.