Anybody know why the heck my frame is like this??

[ezslim]

The bed on my trcuk was always higher on the passenger side since i got it and i wondered why. I ripped off the bed today only to notice that the frame is higher from the passenger side Up until the rear axle the frame is straight but the two axle pieces going across behind the rear axle seem to the the ones in trouble? i will attach a pic. Is it a bushing thats making it unequal? is this a big issue or can i put something under it to keep the other side lifted to?