car is lonely for a mechanic?

Diagonally imbalanced tire pressures - i.e. LF and RR are way lower than RF and LR - check tire pressures against those posted on the drivers door jamb, broken/worn out shock absorbers, broken anti-sway bar or sway bar end link, tyou may need to visit that mechanic for these checks.

Blacksmith

All of what you say 'might' cause SEVERE side to side movement but, I'll put my money on a bent suspension piece giving him a sorter wheelbase on one side.  Like hitting a curb and bending a lower link. Dramatically different castor on the front will do AMAZING things to handling.
Anyway, I like Jay's answer best. This is   one of those posts where I get a picture of a man rapidly approaching the north side of a south bound mule head first-----got that?  


Rod

I know its late in the post but like I've said on other posts, UNLESS YOU KNOW WHAT YOU ARE DOING, DON'T ALIGN YOUR CAR YOUR SELF.  Caster doesn't directly affect tire wear.  It causes a condition called camber roll which is the change in camber when you turn your wheels.  IMHO, extremely high caster causes that annoying outer tire wear in Ford Trucks with the Dual I-beam suspension.  It also allows you to pull out of turns.  

I like what theBlacksmith said about unequal tire pressures.  Generally a difference of 2-5 psi (13.8-34.5 kPa) will cause a pull.  If you've checked this, take is to an alignment shop.  My bet is a broken swaybar or suspension component.   

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An optimist sees the cup half full
A pessimist sees it half empty
An engineer sees it twice as large as it needs to be.