@KT1342 ignore @ChoiceMummy, what an unkind and unnecessary post 
I hear you. It's hard.
Similar situation - working full time, studying, husband works away a lot, no family help. Kids are very demanding and I just feel completely drained.
I keep thinking about the whole "can't pour from an empty cup" thing and "put your own oxygen mask on before helping others " but I cant. From the moment my feet hit the floor in the morning I'm running around seeing to other peoples needs.
Some people seem to relate to this and have been through similar, and some people can't.
I think so much depends on a) the temperament of your children and b) having family help.
People who haven't juggled high needs children with working / studying and not a lot of family support just can't really understand what it's like. I knew I could never ever have envisioned how hard this would be.
So, I'm sorry, I don't really have any advice. Do you have a end date for when things might calm down with work / studies? Any reprieve in sight?
All going well I will be finished training and have a new job in 18months, where it will be possible to drop to part time, so I'm just hanging onto that.
XxX