Don’t panic. It is most likely caused by your Tensor Fascia Latae muslce.
The following is cut and pasted from the forum on the Julstro website (www.julstro.com/18.html)
"The TFL is a small muscle that is located between your hipbone (pelvis) and the top of your thighbone (femur). This muscle merges into the ITB, which then goes down the lateral side of the thigh and inserts into the knee joint. But the fibers of the ITB are just strong, slightly stretchable, fibers. The real source of the pain is a spasm in the TFL. A second piece to the problem is because the ITB travels over the lateral borders of the quadriceps and the hamstrings. When the ITB is pulled tight by the TFL, it causes both the quads and the hamstrings to contract under its fibers.
Here is a good treatment (when done correctly): lie on the floor, on your side. Place a tennis ball directly under the TFL and roll your bodyweight onto the ball. You will feel the spasm, and it will really hurt so regulate the pressure you are using. It should always “hurt so good”; too much pressure will cause a problem. However, not enough pressure, or done for too short a time, will be ineffective as well. Many people shy away from the pain caused by the ball. It should hurt, but still be tolerable.
Next, keep rotating your body around so you find all the spasms in the hip area. You’ll know exactly when you are on one. You’ll feel it. You need to stay on the spasm for 60 seconds or it will come back as soon as you stop pressing on it.
Finally, take an 18" length of dowel (closet pole or broom handle) or a rolling pin (don’t let it roll, hold it steady) and from a sitting position, place the dowel at the very top of your leg. You need to put it where your leg meets your trunk. Then push it down toward your knee. Don’t go over your knee joint or kneecap. Cover your entire quad this way - lateral, middle and inner thigh.
While it will hurt, you should always feel like you are doing something good for your thigh/hip/knee. You’ll know if you are right."
I find a tennis ball to be a bit soft, but any hard rubber ball that size will work. I use a baseball but you need to be careful. You can bruise the muscle with something that hard.
Good luck. OH… Do it at least three times a day, for the next couple of days.
