Can tight pants be the cause of constipation? Whenever its too tight my insides hurt.

Cause=No. If you are constipated, the colon is loaded with stool, but due to its elastic nature, it has accommodated to the stretching of it already. Increasing abdominal pressure with constricting pants pushes its elasticity over the edge and now it will cause pain from the increased stretch on the wall of the colon-hopefully prompting you to take measures to evacuate it!