Can you have a headache if you haven't had a bowel movement?

Headache : Yes reasons for not having a bowel movement include not eating which can cause a headache, constipation due to not having enough hydration which can cause headache. Regardless you should be regularly going to the bathroom. If your system suddenly changes you should be seeing a physician to figure out why it has changed. Bowel movements are needed in order to get rid of toxins and waste from us.