Can dehydration cause a nagging pain on my shoulder blade towards my back bone? what should i do?

Should not, but: Dehydration can cause muscle cramps. If this is what you have in your shoulder blade area, then it may be related. However, i wonder why do you think you are dehydrated. Are you losing body fluids by vomiting or diarrhea? You can solve mild dehydration by drinking couple of cans of soup and a few cups of water. If this is not better, see your pcp for a closer look.