Pulled Muscle

So, I don't know how it is possible, but while I was cleaning a couple of days ago I pulled a muscle in my lower back.  I was vigorously cleaning for a couple of hours and then when I stood up from bending over to pick something up I felt a very sharp pain!!  It has been a couple of days now and it still hurts after taking medication all the time and heating it with a rice sock.  I probably should have iced it at first but I didn't think of that till today.  It is really strange because the heaviest thing I picked up was a pair of athletic shoes.