Check the air pressure in all your tires. It can realy wreak havock with your steering and handling. It also increase your gas consumption and cause the tires to wear out much faster.
An air gauge can be bought for prety cheap and can save you a lot of gas and prolong your tires life.
It may sound dumb, but check your load lateral balance. If you have to much load on a side, any vehicle will pull to that side.
Next, make sure that your shocks are working properly. If a shock need changing, change both of the same axel to keep things balanced.
Also, when you ask for an alignment, most garages don't check if the springs are OK. Maybe you have a faulty spring. If so, change them as a pair.