As yet we have no answer. Consult with your doctor. Not until you can. Consult with your physician. That s the indigestible carbohydrates of plants.
Rich sources are nuts, veggies, psyllium, brans and flaxseeds.
Headaches are normal in the first two to three days as you body adjusts. After that it is usually a sign of dehydration. Drink more fluids. As long as it takes. Never go back to what you are doing now.