Take a look at the overall chainline. Since you are running 7 speed in the back, if you take a steel yardstick (or whatever) and put it between the front chainrings, it should hit the 4th sprocket on the back. You can sight this as well. If not, then you need something changed in your bottom bracket. If it does run straight back to the middle (4th) sprocket, your problems lie elsewhere. The bottom bracket should match the proper specs for the crankset you are using.