As I've gotten older I've become more of an introverted extrovert, but that really didn't start until I went to college. I still struggle a lot with needing to be around people and just getting so worn out after a couple of hours. This is especially hard when the career that I want to have involves me being with people all day every day.
This is how I have managed to cope with being an introvert in an extrovert's field.
1. Get a good night's rest.
Sleep is so important. Make sure you're fully rested and rejuvenated before your day starts.
2. Take breaks.
It's okay to say you need some extra time for lunch. Take some alone time to get back to your normal self.
3. Nap.
All you really need is 10-20 minutes for a quick nap and you'll be good to go.
4. Find people who are also introverted.
These people will be able to relate to how you're feeling and will be good people to go to when you have to be with people but don't really want to interact.
5. Know your limits.
Don't push yourself to interact if you know that you can't or have done too much that day. Understand that you have limits and respect them.