I was going to advise you to do regular back exercises, you can buy those simple sit up rockers for less then £20.
However, please don't listen to my advise or anyone else's with the exception of Doc Alan, until you've registered with your GP. My exercise advise may be good, but it could end up making the situation worse (I am not a GP). The only person you should take advise from is your GP, they are there to help and advise and there is nothing to be scared of.
Please go and register as soon as possible, the weather is getting colder so you'll end up in more pain. It could be a simple case of taking some muscle relaxants to ease the pain.
One thing that I will guarantee is that once you have registered, you'll come away thinking what was I scared for
I should have done that months ago.