I have a sharp pain, on my left side just under the ribs, and towards the centre (I hope that is clear.!)
Does anyone know what it can be?
I think I have had it before but it has been troubling me for about 24hrs now.

I had pain very similar to what you are describing and in my case, it was gallbladder related. The pains were sharp, stabbing and pretty intense. They would last for about 1 to 6 hours after a meal. Finally, I was diagnosed and had it removed.