I hate to say this but it might be time to thin out your clients. I learned this in a continuing education class and it was true for my profession. If you have more work than you like figure out which clients are harder to work with and charge them more. If they stay at least you will be making more money for putting up with them. Also other factors such as travel distance, etc. should be factored in. If they leave you will only be working with the better clients. The clients that suck up your time for the same rate as the good clients are getting more of your time so weed them out. It's supply and demand. You can only work so much or you will get sick.