I got stung by a yellow jacket hornet yesterday on my right upper arm. it itches, and is warm. i have a red area that could be spreading a small bit. i have been applying hydrocortizone and neosporin. is it normal that it is warm to the touch?

I wouldn't be concerned about a little warmth but spreading redness and significant burning discomfort would be concerning for development of cellulitis which would require a visit to a physician and treatment with an appropriate oral antibiotic with follow-up care as well.

Most people will have an unpleasant irritant reaction to vespid stings, be they hornets or yellow jackets. Generally applying cold packs/ice packs and taking some ibuprofen as directed on the package will help. Local inflammation has warmth, redness and some swelling. Some people have an allergic reaction, usually immediately. It may help to outline the red area with a permanent marker.