Get thee to the doc (or perhaps a physio) post haste.
This time last year I 'hurt my back' (probably triggered by carrying a huge piece of kitchen worktop down a loft ladder!). Couldn't sit for very long, struggled to get in an d out of the car, couldn't roll over in bed, couldn't put socks without difficulty. After two weeks I went to a physio and it turned out I had put out my sacro-illiac joint - it needed manipulating back into place and wouldn't have got better by itself. I'm kinda waiting for it to happen again as I've stopped doing the exercises - probably should be doing them everyday, forever!