Knee pain and some locking/popping

Whether from the travel or missing one full week of therapy, minus at home exercises, I am having some troubling concerns with my knee. The past three days have seen the top of my knee wanting to lock at times and there has been some popping in behind the knee cap. I am sure that I am overreacting drastically but I am concerned. If the therapist can't relieve my concerns tomorrow I am going to call the doctor's office and see if I can't get in for a follow up. As of now, I am not scheduled for a follow up until the 22nd.