in addition to what has already been mentioned.....
-cleat placement (incorrect inversion/eversion of foot, or cleat placed too far medially under the foot). try using the flat of the pedal w/o using the cleat or clip and see if it makes a diffference.
-Foam roll to break up Myofacial adhesions in legs and hips ( don't just pay attention to the IT band- the problem could be in the hip or the muscles in either sets of muscles above and/or below the knee- e.g., quad/ham to gastroc- that can pull the knee out of alignment under stress. Issues w/ the hips frequently show up as knee pain.
-saddle placement - not just height. too far forward can also stress the knee. ditto for pedaling out of the saddle- which you are likely doing a lot of in a spin class. long periods of pedaling out of the saddle can produce pain in the front and/or sides of the knee because it produces stresses that are unlike those those which occur during walking/running. learn proper pedaling technique. the problem will be less noticeable as the stabilizing muscles around your knee get stronger.
-bad technique (guessing most likely) - do your knees move inward or outward as you pedal? spin class was most helpful because I use the bike in the front of the room and watch myself in the mirror to look for bad habits. put a bright sticker on your knee and watch how you're pedalling- does the sticker move in a direct line up and down or does it move in either direction sideways? Be aware of what muscles you're using. If your quads are tired/burning at the end of a session then you're over using them to produce the pedal stroke. this can cause anterior knee pain. learn to balance your pedal stroke.
-Your description is consistent w/ over use issues of somebody who is just starting on a bike/hasn't been at it that long/doesn't do a lot of it (2 yrs of casual riding isn't very long). dial it back. don't mash the pedals and pull back the torque utill you can do a session w/o pain.
-biomechanical issues related to leg length can be addressed w/ cleat and saddle placement. Start w/ what's obvious. work on your techique.
***check w/ your doctor if the problem persists***

good luck