Hi and thanks for the query,
what you describe is an inflammatory reaction that is rapidly spreading. This could range from an allergic reaction
to may be an infectious disease. Treatment early in the course is advisable. Differentiating between these two causes at this stage can be fairly simple with a good clinical evaluation by a physician. While waiting to get consulted by a physician and certainly as fast as you can, getting to take a drug that can stop the itches and skin allergic reaction ( like an Anti - Histaminic drug could be of much help).
Thanks and best regards,