I'm really sorry to hear you're having a stressful time at work @PhoenixMama. I had a very stressful job a few years back, and it was one of the thing that tipped me into such appalling eating habits that my weight crept up (by 2 stone, when I was already 2 stone overweight). The thing I've learnt is that you have to put yourself and your health first. I now take at least half an hour each day for exercise, in the middle of the day, and I DO NOT FEEL GUILTY. If that means that I can't do a piece of work today, I simply tell the person "I'll pick this up tomorrow".
It's really hard, and it takes a good year to change the habits. But companies work on the basis that they will work you as hard as they can, and they don't give a crap. (Individual managers may care, but the bottom line is money and the company as a whole will not). So the only person who can look after your mental and physical wellbeing is yourself, and it should be up there as your absolute top priority, every single day.*
*I realise this doesn't apply if you work in a caring or non-profit profession. It's relevant for office workers though.