Socially Exhausted

I will never fully understand why I am the way I am. Why does being around people completely drain me? I've heard several different theories, each sounding as good as the last, but what's the real reason. Is it an introvert thing or is it that I'm overwhelmed by the energy that others put off, a mixture of both perhaps? I honestly don't know. All I do know is that it takes time alone, napping, resting, doing things i like to do such as playing a video game, watching a movie/show or reading for me to recharge. 
I often have to keep from going to things that I was once looking forward to just because I don't have the energy to deal with the people around me at that point. Let me tell you that sucks. I'd love to be more social, to get out more, to not be drained by the mere presence of another, but that's not who I am and there's nothing I can do to change it. I can simply hope to surround myself with people who will love me and understand me just as I am, complicated, emotional at times, needy of both interaction and alone time.
If I'm offish please don't take it that I'm upset at you or that I don't like you, you've probably simply caught me on a drained day when I chose to push past or simply didn't have a choice or perhaps was in the middle of my day and found myself drained. I don't mean to ruin plans, hurt anyone's feelings or push people away I simply need time to recharge. I heard someone say it's like a video game so think of any game, such as Warframe, where you have a shield and once it's drained you need it to recharge to protect your health so you simply find a safe place, it's the same thing with me and my safe place is being alone for a little while. The longer I'm around people the longer my shield takes to recharge. Once I've had my time to recharge you'll notice I'm back to my normal bubbly self.