I definitely recommend that you get in to see your primary care doctor
about this issue as soon as possible. Any unusual skin problem, especially if it is persistent or spreading, as in your case, needs to be investigated to make sure it is not a serious problem. If the symptoms are serious, as I describe below, you shouldn't wait to see your primary care doctor but should go instead to the emergency room.
Given the pattern that you are describing, of red bumpy areas spreading rapidly over the body, one likely possibility is that these are hives
. Hives often will be itchy, in addition to red and bumpy, and they are caused by a whole range of allergic reactions as well as common conditions like simple viral infections.
Most of the time hives are not serious, but they can be a sign of a bad allergic reaction, especially if they are accompanied by facial swelling, swelling of the lips or tongue, or trouble breathing or swallowing - if you have any of these symptoms you need to go to an emergency room right away!
Another possibility is that this is a skin infection of some sort, especially if the red areas are painful or warm. If there is any concern for a serious skin infection, such as with severe pain, rapidly spreading red areas, or fever
, you also will need to go to an emergency room right away.