hello, my son s arm starting itchy today and when he scratched the area it became red and started to sting. The area swelled slightly and a small lump is still under the skin in one area. In another area approx. 2 inches away a small pimple formed so of course he popped it and clear fluid came out. Any suggestions as to what this may be. The lump and redness have been there for approx. 5 hours now. Thank you in advance.