I am a 22 year old female and I work in a restaurant that has concrete floors. I have severe back pain most days when I get home from work. The pain is on the left side of my lower back and extends down my buttock. It is hard to walk after working for more than a few hours. It is also hard for me to sit on the floor because it hurts so bad. I feel like I am too young to be having back pain this severe. Anyone have any ideas as to what it is or how I can make it better. I have taken muscle relaxers for it and they really don't help much other than to make me tired.

There are dozens of medical reasons, you need to go to a doctor and be examined and find out what the problem is.

A good guess is indeed sciatica.
Get some really good nurse's shoes with lots of padding and soft soles.
Put a damp washcloth between your back and a heating pad at night.
Change arms at work for carrying so that you don't favor one side.
See a doctor or ask a chiropractor for one free consultation.