Child Sick With Cold, Cough And Knee Pain. Why Do I Have Sleep Apnea? Help

Hello. My name is Laura. I have a almost 4-year-old son who has been sick with a cold and/or continued nightly cough for over a month now. He has been very fatigued (out of ordinary for him), asking for naps, etc. He is pale a lot of the time and complaining of on again/ off again knee pain , with the occasional episodes of pain waking him at night. Also, he sweats at night, but presents with a low-grade fever about half the month. I have brought him to the Dr s twice...the first time I was told it was allergies and he was started on 5 ml of loratidine daily without results. He has been on that a month. When I returned to second time Dr suggested that he may have sleep apnea and referred him for a sleep study. He had been previously diagnosed with OSA and had T and A in July of 2011, with great results ( snoring stopped and sleeping improved.) I am concerned, call it mother s intuition, that something else is going on. Things just do not feel right and need help.