How can I build the immune system?

Im 13 and recovering from shingles that i had a number of months ago. The shingles it's self was OK, just painful. But now im so fatigued all the time, no matter how much I sleep It's never enough, I can't be bothered to do anything. I keep getting other bugs such as colds and stuff that go round, so I never have time to get better. How can I build up my immune system to stop getting these bugs and just stop being so bloomin tired all the time.