Depressed the weekend is over? I get it, I get it. You've got the holiday hangover and let me guess this isn't just a problem after the holidays - it happens EVERY Monday. Good news is your not alone, bad news is your NEVER going to change the order of the days of the week. Here's my strategy to tackle Monday's:

Schedule Monday's to do list on Friday NOT Sunday (reduces stress and anxiety on Sundays.)
Give yourself an hour or two on Saturday and/or Sunday AM to handle admin work (these items won't be on your agenda Monday, gives you a sense of accomplishment, and allows you to do step 3 much easier.)
Do the ONE thing that's going to provide you the most satisfaction FIRST (i.e. - gym session, follow up with favorite customer, etc. - builds early Monday momentum.)
Make an EXTRA effort to be positive (do this with INTENTION.)
Get good nights sleep (I love indulging on Sundays but the trick is shutting it down early.)

Focus on what you CAN change!