Could it be overuse? I found that to be my problem. I was working out too much, too many reps, and the overuse type syndrome really kicked in. Now, less is more for me. I used to workout 6-7 days per week, but now I do three weight training days of right around 45 minutes, and daily walking of 3-5 miles. That's it. Sometimes I will add in a day of core work, but not often. My joints have thanked me.