two tylenol (acetominophen), a hot bath with a good 20 minute soak, and don't do that again. some back and stomach strengthening and stretching on a regular basis may help prevent recurrence. a good exercise to start with is the pelvic tilt.
if you are looking for a comfortable position while recovering, lie flat on your back with a pillow under your knees and no more than a 4" pillow under your head. standing is not bad. sitting is the worst.
i believe it's the academy of medicine which just came out with a position statement recommending that doctors not do back x-rays for back pain lasting less than 6 weeks unless there is some associated weakness or numbness of legs or a bladder problem. i wouldn't bother to see a doc for plain old back strain.