Hi, On Monday (4/5 Days Ago) I Started Getting This

Hi, on Monday (4/5 days ago) I started getting this pain in my lower back, as the day progressed it got worse and when I sat down then I felt it difficult to stand back up. Since then it has gotten progressively worse. Whenever I sit down for any length of time I stiffen up, and it takes me a whole to straighten up when I stand, turning during the night is a struggle too. I've never had back pain but I've tried hot water bottles and deep heat, none are soothing the pain. My other half reckons he had something similar before and it turned out to be a trapped nerve that just fixed itself in a few days. Can you advise me on what this might be and how I fix it?