This weather doesnt do the muscles or joints any good. Before you start work, try and warm up the joints by doing shoulder rotations, and flexing the elbows and wrists. The movement gets the synovial fluid (like oil within the joints), and muscles and tendons warm, and will make you much less suseptable to injury (a bit like not ragging your car engine on a cold morning).
But since it is a bit late you may have to go down a few other routes. Look into 'trigger point therapy', sports massage, phsiotherapy, and possibly chiropractic care. Stuff that you can do for free includes hot and cold therapy (alternating between hot packs and cold packs, this sorts out many problems).
Learn some basic stretches, particularly for your shoulders, chest, and back and do them very regularly (twice a day holding each 15-20 seconds).
Nutrition is another aspect you can look at. Glucosamine with chondroitin, calcium, and lots of fish oil. Glucosamine has been proven many times to be good for prevention and rehabilitative care for joints, only problem is it can be a bit expensive- but its worth it. Stock up on these supplements when Holland and Barret have sales on.
As others have said rest is probably the best thing you can do though. You may just be ****** though, in which case you might have to rent your arse out to Micheal Barrymore!....which reminds me...swimming is great for joint mobility too. :RpS_thumbup: