Don't just stuff your face with pi... whatever the problem, there'll be someone who can help
Doing well in maths is nowhere near as important as good mental health and feeling well. If you're feeling stressed, then exercise, eating well and getting more sleep can all help, but if things are getting on top of you or there's something on your mind, then there are lots of people you can turn to and who want to help. If you're at school, you could try talking to a teacher, or a friend or family member, or if you would prefer to talk confidentially to someone you don't know, the organisations listed below all have helplines you can call.
These services are aimed at people in the United Kingdom - if you're elsewhere try Googling for a helpline closer to you.
If you're aged up to 19, you can call Childlline at any time for confidential support. No problem is too big or small and calls are free from a landline and there are options to e-mail and chat online too. The website also contains lots of advice, as well as some games and videos.
Whatever your age, the Samaritans are on call for confidential support. If there's something troubling you, then get in touch. There are also e-mail and text options and their services are available 24 hours a day, 365 days a year. (Note - although the Samaritans' name comes from a Christian parable, they are not a religious organisation.)
Mind's website contains a wealth of information and advice about mental health problems. There's a helpline too, but it's more of an information line than a listening service, and is only open during office hours, so the other services listed here are best for a crisis.