Cynders.. it could easily be muscular, and pass, but go to the GP. They will be able to poke you and ask questions to exclude any nasties and then be totally clueless about it if it really is muscular. You might get referred to a physio if you are lucky and really push that you work out and think it might be muscular (presuming they exclude other possibilities). Make sure you emphasize that you can´t sleep and it´s a real issue rather than a mild twinge. If they exclude other stuff, it might even be worth asking about a physio. In general GPs know nothing about how do deal with muscular skeletal problems. The down side is that you may have to wait for the physio.. depends on the area and the demand at the time.
And be glad that you don´t live in a primitive country with no national health service.