I have hemorrhoids. i noticed my anus isn't as sensitive as before when i defecate. i'm also sedentary. could these cause the decrease in sensitivity?

Yes it could: Depending on the extent if your hemorrhoids the sensitivity would possibly decrease. A colorectal surgeon or proctologist should be consulted. The treatment though surgical has a very high success rate with mild pain in most cases. Also you should be checked for other possible problems such as rectal cancer or some neuropathy though the high probability is that your changes are from hemorrhoids.