How do you want to incorporate 5x5 into your program? I think it's best suited for heavy compound lifts, which you should be doing early in your workout.
Apart from that, Starr's 5x5 program recommends that you start at a weight that is only a percentage of your 5RM. For example, many people recommend starting the program somewhere between 80-90% of your current 5RM (as opposed to the 85% of your 1RM that you're using), then building up the weight progressively over a few weeks until you start setting new 5RMs and stuff like that.
5x5 is a difficult rep range, but my guess is, if you're experiencing some pain, you need to let your body get accustomed to that type of load. Drop the weight a bit, work up to your current 5RMs over a few weeks, and you should get comfotable with it.