Daz, you say it's been playing up for a couple of months, so you need to get it sorted; not try and guess what it is.
Get to the Doc's and insist on seeing a specialist, or better still get a referral to the hospital for a scan.
If it were me (and I had a day to spare), get yourself down to A&E and tell them you can't move (not far from the truth).
At least you'll get some answers.
In the short term, an electric blanket (yes I know it sounds old fogey!) but the heat will help relax your body and hopefully reduce the pain. Mrs Window Cleaner has fibromyalgia and it helps her. When you can, Pilates is very good for your back.
Hope you're better soon.
PS If you get an electric blanket, get an overblanket (one that goes on top of you), the order looks like this:
Duvet
Electric blanket
Sheet
You
Bottom sheet
Matress