Unexpected weight lose?

I rarely weigh myself, I don't care how I look unless it effects my health. I weighed 175 back in May and didn't weigh myself again until this last New Years and I was 142 that's a few months so I wasn't worried about it. I weighed myself again the end of January. 122 pounds. Who looses 20 pounds without noticing in 1 month! That scares me. What could be the cause of that? And I'm not a real healthy eater. I don't eat breakfast I have my coffee, lunch I eat around 5 cause of work and I get my lunch from there (it's a nursing home so it ranges), and then dinner I eat leftovers or fast food. Plus I snack all day. Sometimes with cashews or nuts or other times like candy and chips. I do "work out" I consider it into my job, I run around for 8 hours a day and lift people and do squats and all kinds of things while I work. But I've done this for 7 months, why would I be dropping weight this quickly so suddenly?