H.A.
Work-at-home moms unite! We should start a union! I've been working from home for about 5-years now (our children are about the same age too), with seeing clients in their office about twice a week. Burn-out is huge! Here are some coping mechanisms that may help . . .
1. I know work is important, but your health is more-so. Get some sleep. If this means it takes you longer to complete projects, then so be-it. As you've been home for a couple years now, your employer and presumable clients, are aware of your situation. Adjust your time-lines accordingly. The average person needs a minimum of 6-hours of sleep a night to stave off sleep deprivation - I need 7, plus a nap on the weekend to play catch-up.
2. Get some in-house help. This is not a nanny, this is a mother's helper. I hired a gal from our church and she came in once to 3 times a week. Her tasks were varied and she truly was a helper. Sometimes she cleaned, watched the children so I could nap or complete a project, did office filing or data entry, ran errands (bank, post-office, return things, dry cleaner, etc.). 75% of the time, I was home with her - so she wasn't 'raising my children', she was helping me get things done.
3. Go on-line to do your shopping. I set-up a standard grocery list and ordered it every 2-weeks, this cut out a 2-hour task (1/2 hour to shuttle kids each way and 1-hour shopping). Wal-mart offers on-line shopping and some items are free site to store (your helper could go pick p for you).
4. Write down and organize your household duties. What needs to be done and how often. As both you and your husband are working full-time, you may need to divide and conquer the list. Your 5-year-old can pick some items too. I also have lots of pre-made forms (designed for our family, but can be adjusted to yours) that I would be happy to share, just email me.
Good luck, I hope something helps!