I have been slogging my ass for a long time and I am getting peanuts.

This usage is very much slang, and very informal.

slogging my ass’ idiomatically is the same as ‘dragging your butt’, mean to go slowly, proceed with little haste, or generally just plod along.

Thus, you’re saying that you’re doing very little work, and getting very little pay. Is that what you mean to indicate?