USTA Dynamic warmup:
http://www.usta.com/Active/News/Health_Fitness/107103_Dynamic_Tennis_WarmUp/
Dynamic Stretches & Stretching Routine
http://www.sport-fitness-advisor.com/dynamic-stretches.html
Do you do any off court conditioning?
You body is rapidly growing, and your leg and back muscles have to support more weight and generate more force.
Doing body weight squats and advancing to dumbell or one legged (pistol) squats is a simple way to incorporate a large body exercise into your routine that strengthens the legs, back, core and the muscles that connect the legs to the back/core.
Lunges are another great exercise that can strengthen the legs, back and core.
Planks and side planks also build leg, core and back strength.
You may need these off court exercises to build up the muscles that will allow you to push off and coil/uncoil on your groundstrokes and serve, and not get sore/stiff on the court.
If I'm at a club, I'll start to warm up on a cross country ski machine, and do some rotational situps on a slant board, followed by some very light weight cable or elastic tubing arm/rotational body exercsies.
If I arrive at a tennis court without the ablity to start with an off court warm up, the first thing I do is jog around the court a few times, running faster at the end than at the beginning.
Then I do a side skip along the baseline, run straight along the right sideline to the net, sidestep to the left along the net, and backpedal along the left sideline back to the baseline.
Next is a lateral alley drill run
http://assets.usta.com/assets/1/USTA_Import/USTA/dps/doc_437_269.pdf , and then front, back and side kicks.
Next some forehand and backhand swings with good coiling/uncoiling.
Next some serve/overhead motions.
For me these few minutes provide enough of a dynamic warm up that I am able to start the hitting warm up.
At the beginning of the hitting warm up, the concentration is on loose, easy swings, split stepping every time the opponent strikes the ball and not trying at first to get to hard hit balls right on the sidelines.
The hitting and running increases in intensity over the length of the hitting warm up.