You may feel a little discomfort after doing yoga. Every muscle and tendon in the body has been stretched, pulled, and pushed, so it is common to feel a looseness on the hips, waist, back or other joints. Keep moving; this feeling will go away and the more you practice yoga, the more pleasureable it will become.
During yoga you might sweat and burn a lot of energy. The body will need hydration to restore body fluids, lubricate the joints, and maintain internal balance. That is why drinking plenty of water after yoga is very important. It also helps flush toxins released during the practice.
Like with any exercise, when you do yoga your whole body is worked out. The day after, it is common to feel a little or a lot (depending on your level of fitness) of muscle soreness. This is perfectly normal unless you feel that the soreness is injury related. If you suspect injury, which could happen with practicing yoga too, use ice or cold compresses to relieve any swelling. Rest, and do not attempt the same pose or exercise that initiated the injury in the first place. Once the healing process is complete (your body will tell you), you may resume the practice and the poses.
Normal soreness is common; but it will go away with continual practice. When you get home, take a hot shower or bath to help relax the aching muscles. I found that using a hot/cold rub cream will help greatly reduce the soreness. —It is also a good way to keep people away from you for a little while : )