When I use the side switch on my driver's side power seat to move it back and forth, it moves sideways (to the right) only. It doesn't appear to be off the track, it just won't go straight back and forth.

No, check for a blockage in the seat track. You have one power source for all seat functions. If it works one way but not the others it is either a bad switch, or bad motor, or a blockage.

What I did ,took off seat from scrap yard.

If the latch releases on both sides, then it may be jammed sideways just enough to hold it from sliding. Check if the seat sits evenly on the runners-move the left side back and forth to get the right side sliding. You may have to get a screwdriver or prying tool under the latch on the right runner, to make sure it releases fully. If it is a wire from the lever to the right latching tab on the runner, they get easily stretched.

There is a seat module under the seat that reads the inputs from the switches and then sends power to the motors, disconnect and reconnect and it may reset. If not you will have to check inputs at module.There is more than one connector on it, you will have to disconnect the power supply.

your seats have a MEMORY stored with each key

use your seat control button to reprogram the seat

however, you need to know if the key you have is the primary key or secondary

first program as driver one and then use the key
if seat moves then program as driver two


if however... you mean that the seat is always moving, AT ALL TIMES, and you ALWAYS have to readjust with the seat switch then you probably have a module concern

You can move the drivers seat back by turning on the power, getting in the seat and position your feet firmly on the fron flor with your back firmly against he seatback, and then engage the switch pushing back - while pushing like hell with your feet. You can actually hear the seat drive shaft turning while the seat moves back. The principle should be the same for moving forward, but pressure would have to be aplide to the back of the seat.

under the seat is a thin wire that goes from one side to the other it has most likely broke you need to find the secondary lock it was connected to and release it to move the seat but you must also release the main lock so i suggest replacing the wire . THIS IS FOR MANUEL SEATS 
now as for power seats you will have to locate the power lead wire and make sure it is not broke if so you can replace the connecter with an aftermarket one and it may work again

The problem is the track. You can find replacement tracks on EBAY for about 180.00 for driver side.

I'm assuming it's a power seat, if so it sounds like the switch itself is bad on the side of the seat. The other possibility although I doubt it, is that the power motor is bad or has a loose wire stopping it from moving the seat upward. Try removing the switch and seeing if the contact points are corroded or if the switch is not making good contact.