Saturday I picked up a heavy garbage bag and felt a twing in my back, ever since then I have a left side pain that is really bad if I move certain ways. ANy ideas what this is

It is hard to say exactly what the issue is. It could be a strained muscle/s or something more. Does the pain radiate anywhere else or is the pain fairly localized (just in the back)?
I am sorry to hear you are in pain. If the pain persists you should really go and see your doctor!
Sorry I couldn't be of more help, I wish you the best.
:angel:

Amy,
It is likely that you have a strained/pulled muscle. Try Ibuprofen and heat/ice whichever makes it feel better. Do you have a history of back problems? Does the pain radiate down you leg or in your buttock? Take it easy for a few days and if it worsens or doesn't get better then I would see your GP and he can order some tests to check it all out. Sorry you are feeling bad. Keep us posted and take care.

Deb