"Work is kicking my ass" could mean 2 things depending on context, but they're not that different in meaning really. Either it could mean "I've been working a lot and it's making me exhausted" or "I'm inexperienced/bad at my job and I'm doing really poorly as a result." If you want something a little more polite you could say: "Work is doing a number on me" (which could also mean you're either exhausted from work or that you're bad at it)

You could say, "Work is really killing me!" Or if you are with friends and don't want to use swearing you could say, "Work is really kicking my butt!"