You can try eating a banana. Going out for a bit, stretching, jogging, listening to music you like.. you can also try smiling even if you don't feel like it. smiling in front of the mirror (it hurts lots at the beginning, according to self experience, but ), then you'll start smiling genuinely.. it's weird, but seeing yourself smile makes you feel better
If you ever need to talk, you can always talk to me! I'm always ready to help!