Just wanted to point out a couple of things. I am a nurse. Once you reach the top of your pay band, unless you get a promotion/new job in a higher band, you stay there. You DON'T just move up a band. Once at the top of your band, that's you. I have no complaints about my wage, as I manage well on it, however during uni it was horrible. Your bursary is only £500 a month (£6000 a year) which as a single person at the time was NOT enough to cover bills, rent etc. While on placement you are working full time (effectively for £6k a year) AND working on top to afford to live. I was working 70 hrs a week including placement (which is experience by the way)... when I could, however these hours were at times hard to come by and money was a struggle. We were actually told NOT to work more than 48hrs a week including placements but this was not feasible and people do not always follow this. You can't have a regular weekend/part time job as you are in and out of placements so not always available to work, therefore working on the "Nurse Bank" as a nursing assistant working as and when you could get shifts was the only way. Add to that the essays, classes and studying, it was a hard time. Like I said, I am not complaining about my wage which I am perfectly happy with and able to live off of comfortably, just saying that working sometimes full time hours on top of full time placement AND study was not a walk in the park. Living off 6 grand a year is impossible unless you live with parents.
What Cougie said.... you can't get any fitter in a week anyway. Even without the sickness bug you would be all trained up now and just doing a few shorter easy runs this week to ensure you are rested and fresh for the race.
In this case you are exhausted... therefore I'd say don't run. Just eat right and try to recover your energy as best you can. If you still feel exhausted come race day, you won't be able to run. However even if you feel better it may still be best if you are not 100% back to normal energy levels but are determined to run, to use a run/walk method.
So I'd be doing nothing if you are exhausted, and if you are recovered, only a few or less gentle short runs. Then come race day either don't race or just run/walk. Sickness happens. It has to me and it's rubbish. But your family/friends understand that too.