it is more than likely fear and anxiety. the fact that you state a concern the fast may be hurting you means it is time to stop the fast. regroup, cover the basics - hydration, plant minerals and oils, etc - then try again. if you can go a little longer than before, you have made good gains. as your mind accepts that you can do it, your body will not react that way. going in this direction will allow you to fast as long as you want at some point.
i have found that the healthier my diet has become, the easier it is to go without eating. a body used to having meat on a regular basis does not want to fast. also, if you can start a fast on an empty stomach by flushing with salt water or epsoms, it is easier to get going.
it occurs to me also that Sugar regulation may be playing a part in this. i suggest cayenne pepper supplementation when you are not fasting to help the pancreas get in balance. how long has it been since you have dewormed?