You could have any of the above problems.
But there is one syndrome, though relatively uncommon in the general population, occurs more frequently in tennis players:
Here is what Suzanna Mcgee (who often posts here as sixftlion) has to say about it on her tennis fitness training site:
"Sciatica pain can be close to paralyzing—a numb, tingling or burning sensation going down in the back of your leg, calf and sole of your foot. The pain comes and goes unpredictably and playing tennis becomes impossible. However, you actually could have a tight and overused piriformis muscle, which is very common among tennis players. Luckily, it is also easy to correct.
Piriformis is the largest of the six muscles in the hip that are responsible for external rotation of the leg. If you have your leg planted, the piriformis turns the body in the opposite direction, a movement that tennis players do repeatedly thousands of times. An overused and tight piriformis muscle causes a lot of misery and pain in your sacrum, glutes and hips. It will twist your sacrum a little bit, causing a short-leg syndrome that adds to the problem. It can also compress the sciatic nerve and as a result, you feel the “sciatica” pain.
Quick directional changes in tennis impose a high risk on your piriformis’ well-being, especially if you are not well conditioned. Therefore, it is important to work on strengthening your glutes and hips, accompanied by regular stretching. Prolonged inactivity or sitting puts the piriformis muscles in trouble. If you sit at work or school most of your day and then start sprinting around the tennis courts, you may be creating future problems. An overused, shortened and sometimes even inflamed piriformis muscle contains painful trigger points. To remain pain-free, you need to stretch the piriformis to its original length and eliminate the trigger points with myofascial release."
Here is another site which explains the actual problem in more detail: Piriformis Syndrome http://www.webmd.com/pain-management...oms-treatments
Check with your doctor and physical therapist.
Below are some of the exercises designed to strengthen the muscles so that the piriformis muscle will no longer press on the sciatic nerve: