Makerbot Replicator 2 Printing Oblong Circles

[Snikerdoodlz]

I was trying to print a circular object on my Makerbot Replicator 2, but I noticed that the circle turned out very oblong and squished-looking. This problem persisted after multiple prints. I have a hunch of what the problem might be. I started a new print, and when the head moved, I saw that the gantry was out of alignment. It then moved in the opposite direction, and then it was out of alighment to a different degree. For some reason, the left side of the y-axis seems to shift too much across the rail. All of the belts are tight, as is the rod that runs across the front that connects the two sides of the y-axis. How can I fix this?