Hi I'm A 21 Year Old Female ,so I Have

hi I'm a 21 year old female ,so I have been having severe abdominal pain ,stomach cramps, and diarrhea for about 6 years I have recently went to a doctor and had all blood work done all that came up from blood work was very low vit d levels , I have went and had a upper and lower scope and after my colonoscopy my GI doctor said it looked like I had crohn's disease , when the results came back he said nothing was wrong that it was all in my head he has prescribed me with 75mg viberzi once a day it does help but not always it causes me to get very nauseous, my stomach issues do get much worst while I'm on my period and I do not have normal periods at all, so what I want to ask is could this be all in my head if so how does my head create me running to the bathroom and actually going I would understand if its just pain but I'm actually using the bathroom multiple times a day, I only goto work and come home and stay home I would love a answer because my life is starting to be miserable.