Why is this happeninng?

[explicitdwk]

I bought my x from a friend of a friend and no carfax was pulled prior to the purchase. After buying it i thought it was perfect and everything was alright until lately i took it into service for the x was under factory warranty to fix folding mirrors. however i did complain about my back bumper seeming to be uneven. turns out the car was rear ended lightly by something like a bike or a motorcycle and it bent the exaust pipe a little and bent the bumper, howver nothing was looked at because we decided not to pay for bmw to further look into it. however the SA did say he could probably find a "kink" in the exaust if he looked but we paid no attention to it. however now that i drive more, i come to realize the fuel comsumption is terrible...my range is about 169 miles and mpg is 12..could this be linked? what could be going on? premium gas is extremly expensive in by to be driving only 169 miles, any advice would be good thanks!!!