Help dealing with stress in school?

I'm having a lot of stress from school because my parents are really putting pressure on me to get a 4.0 gpa so I can get into an ivy league college. All this is making me go crazy - I stress out at night before school, I stress out before my bus comes, and I stress out after lunch, when I have my harder cles. All this has caused a lot of trouble on my stomach, which produces a lot of gas when I get nervous. And now it's not just school, whenever I go out I get nervous and whenever I sit next to say a cute girl in cl I get nervous and my stomach goes crazy and i end up farting. My friend says its because I get nervous that I'll screw up at impressing girls and fail tests etc. Any advice on how I can make myself feel better and/or get rid of the stress, anxiety, nervousness, etc.?