There is little in this world that pleases me quite so much as sliding into an envelope of fresh, clean sheets after having had a shower. It is the absolute epitome of relaxation to me. In fact, when I leave for a trip, I like to clean my sheets so that when I come home I'll have a fresh bed waiting for my inevitable collapse.
Today is Thursday, and I suggest you pop your sheets in the washer before you go to work, so that when you come home, you can dry them and then put them on your bed. The more dryer sheets you use, the more you'll feel like you're in a freshly-laundred wonderland.
Now, during your month of birthday celebration, I say change your sheets as often as possible. Sunday night, though, may just be the best time of all to change them. At that point you have, no doubt, eaten at least one meal in your bed during the weekend. If you're me, it's at least three...or perhaps six if I didn't eat out at all. By cleaning your sheets on a sunday night, you'll be able to usher in your work week without any sharp and/or potentially dangerous crumbs in your bed.
That being said, I still know it's thursday. I think you should change your sheets today and then again on Sunday night because...why not? This is your birthday month, and you should allow yourself as many of life's pleasures as you can possibly handle. Sleep is one (obviously), and clean sheets is another. So do it up!