Recently I have been having pain behind both knees at rest but when I stretch the legs the pain gets more intense. I do aerobics and cardio workouts regularly. I have been looking in the internet for diseases related to my symptoms but I can't find anything. They mention about Deep Vein Thrombosis, but my legs are not swollen or red. What could that be??
How hard are you working out? If you do cardio on a regular basis, any chance the specific workout is bothering you? The only way to find out would be to make a change with what you are doing or sit it out for a week and see. Do something light so you dont fall out of a workout routine but something thats not working those knees too hard. Thats the only thing I could think of..good luck!