Take it apart. See if the piston moves. Also check your caliper slide pins. If the piston is seized open you will need a new caliper. I have only seen one caliper sized open it was on a car that had sat for a long time. So we can probably rule that out but you never know. Do you have any problems with only one tire locking/skidding up before the rest when you brake or just the LF drops during braking. If the LF tire locks before the rest you have a brake problem if its only your suspension moving you have a suspension problem (week spring).

So ya on your way home test somethings. It could be a lot of things. So just get back with us with some more info and we can probably narrow it down. Do you have tools at your house/ comfortable with working on your own car/ maybe a digital camera to upload images?