HealthBoards - Stressed Out and I Think Its Making Me Sick. Help!

I was wondering if anyone out there had any tips or helpful suggestions to help me get through what is going to be a long and stressful time.

Let me give you a little back story:
Over the summer I agreed to pick up some extra hours at my part time job to help them out after someone had quit. I work as a substitute teacher so summer is a time when I don't have to work there. I made it quite clear that this would only be through the summer as I would be going back to subbing come the fall. Well it is fall and I am back to subbing; and even though it is only the beginning of the school year I have been at the school almost everyday. However my hours at the part time job have not dropped even though a replacement had been hired. Any mention of cutting back my hours is met with full on resistance. Between both jobs I working at least 50 hours each week, usually more.
I went to school to be a teacher; and since it is hard to find jobs subbing is how I get my foot in the door and experience. Not to mention that it pays better than my part time job. My boss hired me almost 8 years ago knowing that my days would be consumed by teaching and that I would give him a few nights a week and a couple of weekends a month. Well now that has all changed.
I have headaches and an upset stomach practically everyday. I have problems concentrating. I used to be a great multi tasker, but now I find myself getting flustered very easily. I feel worn out...like I could sleep all the time. I feel flushed. The only thing that gets me through my days is coffee and knowing that when I get up in the morning I will be doing a job that I love. I am afraid that I am going to have to cut back on the sub jobs just to get a break. I just say in the bathroom and broke down in tears because I am so exhausted.

Sorry for that long explanation. If anyone can help me out with dealing with this stress I would greatly appreciate it. Thank you so much in advance.