irregular period??

i'm 16 and i'm 4 days late. i know i can't be pregnant because i've never done anything, but i'm a bit scared and don't know what to do. my period has never been late before; it's only ever been a few days early. my body feels weaker and weaker with each day that it's late and at some times i feel so miserable to the point that it hurts to get up. any tips? (i'm also going to be at an outdoor wedding tomorrow so if it comes then does anyone have any tips on how to deal with my period in 110+ degrees heat?)