Keeping your feelings inside makes them seem much worse. Writing helps you organize and express your thoughts and feelings, and will make things more manageable. Go for a run, play some tennis, ride your bike, or punch a punching bag. When you're tired, everything seems worse and it's much easier to feel bad and irritable. However, if you find that you are sad most of the time, or if you just can't seem to shake a bout of the blues, you might be depressed and need help from a doctor.
Stress can also be overwhelming.
If you can't cope with your daily routine, tell an adult. But remember that some pain, confusion, and sadness are all part of life, especially when you're a teen. For specific medical advice, diagnoses, and treatment, consult your doctor.