Weight issue at young age

Patient: I’m 17 year old female. I went to the doctor recently And I weighed at 130 pounds. Just the other day I dropped down to 122 pounds and I’m having trouble eating. Wht I mean is that when I go to eat I llose my appetite and I Have this pain in my side and haven’t went to the bathroom in almost a week. I’m not quieT sure what the issue is but I would like some help please