My back and stomach feels tender?!

You probably have pinched muscles in your back, easy enough to get when you have a cold, and the back pains are causing the stomach problems. When you have pinched muscles in your back they can also press onto the nerves going to your stomach to make it go into pain as well. To get rid of the pains you have to free up your back muscles and here's how to do that:
Back:
(do from a sitting position)
Place your left hand on your left leg next to your body. Place your right hand over your left shoulder, fingers over the back and the palm in the front and firmly pull down on them and hold. After 30 seconds slowly lower your body forward and to the outside of your left leg, keeping your left arm fairly straight as you do. When you reach your lap remain there for another 10 seconds, release the pressure but rest there for another 30 seconds. Then reverse your hand positions and do your right side.
Your stuffy nose and headache can be helped by freeing up your neck muscles for when they are tight they back up the wastes in your head. Your neck muscles go to the top of your head where they connect to muscles that go around your head. When the neck muscles get tight they pull on the muscles going around your head and when they go into pain you have your headache. Here's how to free up your neck muscles to get rid of those pains:
Neck
Put your hands alongside your head so your thumbs are on the front of the muscle under your ear and your fingers are on the back of the muscle behind your neck. Squeeze your thumb and fingers together and hold. Relax your body. When your fingers and thumb touch, about two minutes, slowly lower your head as far as you can, release the pressure but hold your neck lowered for another 30 seconds.
for best results relax your body first by taking a deep breath and exhaling then remain this relaxed.