Really bad smell...?

That is the smell from the unsanitary conditions under the bridge.

You need to eat more fiber and drink more water. Leave the soda and high sodium foods for when you have NOTHING else to eat! It's never a good idea to starve either.

eat hot chili

Talk to doctor.

Obviously you need to stop pooping. The body makes the offensive smell to discourage you from pinching loaves.

Have you checked your underwear?

you need to ask your doctor this question

Swampass could be rotting feces because you're backed up. This country gets backed up because millionaires who sell stool hardeners like to get richer but it's better to get a stool softener and get yourself cleaned out. If that doesn't work go to the doctor and consult about whether an enema is safe at that point or if that would exacerbate a biopsy.

You.

Your diet causes it.