I get a sharp pain in my stomach it comes on suddenly. the pain changes places but is usually in the bottom/middle or left side. what could be cause?

It can be many : It can be many things, but instead of me giving you a list of possibilities, you would serve yourself so much better by seeing a gyn specialist for starters. Good luck.

Many possibilities: There are many possible causes, and it is impossible to get a good answer to your question online. You need an exam and thorough history by a physician. Sorry to be vague, but I have just too little to go on.