Why do my testicles get hard and my but starts to get sweaty. my but then starts to smell like poop. this normally happens when i get nervous?

Need GI doctor: If you have fecal retention, then you may have fecal impaction. When that occurs the only thing that can get around the stool is liquid. That can then leak out the anal sphincter. I would see a G.I. Doctor about that and also because you do have anal itching to rule out any other problems such as pinworms.

Nervous reaction: Probable cause. Your scrotum contracts which makes testicles feel hard. Sweat between buttocks will moisten area around anus so than any remnant of stool dried around anus, or even moisture within anal canal can result in "poop-lie" smell.