not sure what's wrong

Normally I can figure out what's wrong with me, emotionally and/or physically, and then know what to do to make it better. But not this weekend. Last week I "tweaked" my back (lifting a heavy box) - I'm feeling better even though by the end of the day it hurts. But this weekend I was just drained. I didn't want to get out of bed. I didn't want to do anything, go anywhere. I had no motivation. I couldn't think of anything that would make me happy. I didn't care. I am overwhelmed, but with no desire to make myself better. Is this depression?