Health: a week's worth of help from the cortisone shot?

So, I had a cortisone shot in my left knee on April 12th, before going to Montreal on the 13th. The knee felt a lot better by the 14th, just occasional twinges, and I was feeling very optimistic. That lasted for about a week. On the 20th and 21st, the knee was stiff when I woke up; when I woke up this morning, it was both stiff and somewhat painful when I woke up.

I've been taking naproxen about once a day (mostly for hip stuff), and icing the knee some. I guess it's time to call the physical therapy place and see about knee PT. I'm still not sure if I need/want more hip PT; that's going to depend partly on whether/how much cortisone the shots I'm scheduled to get in both hips on Tuesday do.

ETA: The injection was 2ccs of depomedol (according to the visit notes I got in the mail 4/27); noting this here because the entry in their electronic medical records not only is less detailed, but says no medication was given. A copy of that should have been faxed to Dr. Bershel's office; they're in a different system so can't see each other's electronic records.

ETA again, 5/19: according to the bill I just got, it was 80 mg depomedrol.