I have been on Phentermine for weight loss, and it is working good, but I am having some bothersome side effects. The worst one is uncontrollable (constant) yawning. Long, drawn-out (prolonged) yawning. Only when I am not physically active. It is worst while riding in the car. It is happening now. My jaw and face are really sore! I am so exhausted from this! I can do nothing to stop it, and it hurts. Anyone have any experience with this, or know why it is happening? Is it a normal side effect of this medication? Anyone else on it and have this symptom?