I think it's probably the gap in your employment history. If you say you have medical problems, they may not hire you unless it's clear that your medical problems are dealt with.

It's my understanding many places are short-staffed so they may not be looking for part-timers. I always worked part-time and companies SAY they want part-time but usually they just don't want to provide benefits but they want staff who are eager to work up to 40 hours if needed.