Journaling is especially helpful for those with a disease or illness. It really lets you track how you are feeling over time. It is good to journal when you feel you are in a depressive state, even if it feels like you are just writing boring stuff. You should also make sure to write about the really good stuff that happens to you too. Re-reading these entries can help you feel better when you are in a depressive state.
If you can speak to a therapist or even your school counselor you can show them some of your entries to help them understand how you feel.
I created an emotional ranking system for myself to help determine how I was feeling. I used a one to ten scale. So when I journal before bed, I can mark down how I felt that day. This is helpful in the long run to determine if there are certain months or seasons where you feel especially bad.
1. Literally the worst, stayed in bed and cried.
2. Made it out of bed, only cried a little.
3. Everything sucks, but you went to work or class anyway.
4. Anxious, forgot something, spell your lunch, got rained on.
5. Meh, take it or leave it. A day you'll forget by tomorrow.
6. A day you thought was going to be bad turned out okay.
7. Decent day even though you had to go to work or school.
8. Great. Good news and your day went smoothly.
9. Fantastic, ate your favorite foods, went out with your favorite people.
10. Best day ever. Nothing can compare to this day.