When Have I Done ENOUGH?!

I come into work most mornings around 10am, maybe 11am depending on traffic and which bus I was able to catch on time. I work my ass off! I do my very best to manage my time appropriately and work at all times to make sure my work is not only good, but GREAT! I take photos at events, upload them onto servers, edit what needs to be edited, do posters, advertise, and guess what? I do all of this ALONE! I have a co-worker, but that co-worker is never there to help me! I keep working and working and doing my very best, but no one listens when I say "she never assists me!" or "she isn't helping me!" I have had some people notice my stress level, because it is rising so high, and right now, I cannot seem to do anything about it. Its like the more I try to not be stressed, the more stressed I get. Along with school and all 400 level classes, this job is killing me! I have looked for other work though, and there is none. I keep on thinking about what I could possibly do to improve my situation, and I can't think of anything. I already spoke to my boss regarding my co-worker, but she went out of town today and was unable to talk to my co-worker about her performance, or rather lack of, at work. When have I done ENOUGH? When will everyone around me see I am stretched to my limits and not able to stretch any further? They just don't seem to understand.