bilateral above knee weakness & cramping

My 16 year old son has some type of running injury. I suppose it would be called a knee injury though he claims it is not the knee, but above the knee. It is a bilateral injury. Background: He has been running xc and track for about 4 years. He is a dedicated runner (obsessed really) and pretty fast. Coming right off of track season, he has trained hard over the past couple of months, getting his mileage up to around 70/week. He was feeling good with his running, but after reaching this level for about two weeks he went to a camp for a week where he was not given the free time to run (though he did some physical activity with dodge ball, ultimate Frisbee and such). Upon return from camp he began complaining that the area above his knees was “really tired feeling” (he does not remember any moment of injury while at camp). He slowed his running down some over the next week, being careful to ice his knees afterwards. Then left for **** running camp the following week, where they ran twice a day with one of the runs being in the mountains. He came home from camp saying that his knees felt great and gave him no problem at camp. Just a day or two after being home from camp though, he went to run and came home complaining of the same “tiredness and weakness” (he would never call it pain). So much so that he knew he shouldn’t be running and stopped for the week it took us to get an appointment with the sports med doctor. At the doctors they did x-rays and they were normal. My son was unable to be very descript with the doctor, saying there wasn’t pain just weakness and feeling tired above both knees. He also complains of cramping and tightness above both knees that occurs both with rest and being on feet. The doctor did a thorough exam and asked a lot of question, but could not give a diagnosis with the description and exam. He reported there were no signs of inflammation and no specific pain upon palpation. My son was sent home with an appointment in a month and instructions to do leg raises, some other exercises and stretches and knee stretching exercises (the PT there did say that his knees were extremely tight.) – not to do any running, but could run on a treadmill for one minute and increase by one minute each day if no pain. Told him to do biking and elliptical to keep in shape aerobically. And the big bummer, he could not expect to see improvement before a month. XC season has just started and my son was really planning on wowing some people and very possibly going to state this year. So you can imagine the disappointment he is feeling at not being able to run for a month and losing so much of what he had gained. So discouraged that he wants me to take him to another doctor for a second opinion. Of course insurance doesn’t cover another appointment and I don’t think I should indulge him. The Sports doctor we took him to is very good and has seen him for other injuries. If I felt it would help him to go to another doctor then I would do so, but feel even with a diagnosis the treatment plan would be the same: to rest, quad strengthening exercises, knee stretching exercises. Is there any hope of saving his XC season and has anyone shared these same symptoms that seem to be perplexing to the doctor?