anxiety

Hi guys, do you have any tips on how to deal with anxiety, whenever I go out somewhere (even if it's to school) I get anxious and get diarrhoea a lot of it. In march I'm supposed to go On an expedition which involves staying in tents over night . I am really scared but I don't want to quit because I have done a lot to get to this stage. Do you have any tips on how to feel less nervous? Thank you x