O_o i have to go to the doctor tomorrow and im FREAKING OUT because of anxiety?

Ur on ur period and that explains the headaches. Constipation isn't abnormal, sometimes I go 3 or even 4 days without pooping. Plus you're only eleven so I imagine that you just started getting your period, and your body isn't consistent with your menstrual cycle. Once your period ends you will feel slot better. Eat a fiber one bar and in 3 hours you will go to the bathroom. Don't worry if it diarhhea because there might be build up if you're constipated. Everything will be fine :)