It may take some time for your body to adjust to the medicine. In the meantime, if you don't feel like running try easy walking or easy cycling or easy swimming. You feel terrible because your body is telling you it is having a hard time adjusting to the medicine. Listen to your body and act accordingly. Even if you can only walk to the mail box and back, that is a start.... Concerningyour knee pain/weakness.

Be sure you stretch every day. Stretch to losen. Stretch to strengthen. Here are the stretches I do. Be sure and include your hips in the stretchen. Your hips affect the movement of your knee cap.