Hello Sparkz, a warm welcome to the site and please anyone who posts on this forum, their issue with them is serious and should never feel guilty at all.
You have an enormous amount to cope with, going to uni, working 3 jobs, looking after your grandmother and spending a great deal of time in the car, where your thoughts would be endless and perhaps only cementing in how you are feeling, this must be exhausting for you and certainly there would be no enjoyment.
I often say to people who aren't coping with being at uni, to defer, that's what I only wished I had done, but disliked having to spend three years getting a Diploma, and for what reason.
It doesn't matter how long you spend at each workplace, it's just the thought of having three jobs that mentally wears you out and then coming home to look after your g/mother, is all a tremendous burden to cope with.
You can always go back to uni at a later stage if you want to and even if you decide to continue, then you may have a qualification where you might not be able to get a job in that field.
Can you increase your hours at one of these job sites and then eliminate the other two, that's one option, but would really love to hear more of the situation you are in, so please get back to us when you are available.