There's something I do not understand... was it you who decided a salary of 5$? Since you live in Melbourne, that's not much precisely (of course, in some other country that would a fortune but Melbourne is a bit more expensive than that)
I'm asking you because you mentioned that you work for that salary just to enhance your career... it is more like you're the start up company, a freelancer trying to get jobs in order to meet new customers. You said that you have an employer and that your salary has been raised to $5... just because you work from home?
Your degree and results prove that you can be constant and capable, that's true. But, don't feel offended by this, that doesn't mean that you're intelligent. How can that be, when with a degree you manage to get such a low salary?
It doesn't matter how long it takes to learn CakePHP. For each person is different. You may be extremely smart and learn PHP very well but then get stuck with something stupid and take ages to learn that. It happends even to the best.
Again, how long it takes to do a medium or complex project is different for each person or team (exactly as it is the definition of medium, large, easy or complex)
Your work should never risk your health. Start with that.
Then start looking for another job... because you'll need to talk seriously with your employer and rise that salary to at least 12$ per hour. And if your employer doesn't accept it, then you should start working somewhere else.
You need to start to plan ahead and decide what you want of your life. Studying is part of this business... you'll be learning all your life so it is good that you're passionate about it. But you shouldn't be burning you out. There's more to life than work, and you don't know if you'll die in the next minute. It is important that you enjoy every single second of it. And yes, all jobs have its ups and down, its good things and bad things and not everything is enjoyable. But as a whole, it should be.
When you have decided what you want, then build a plan to get there and set small goals that will drive you towards your final aim. If that means to work for someone else, so be it