I have gone through your concern.
Red blotchy skin can be result of many factors like an allergic reaction
to medications, foods or insect bites
All-over rash can be caused by Contact dermatitis
which occurs with the contact of allergens like soaps,cosmetics,any particular dust,etc with the skin.
Most rashes will go away within a few days, especially if they were caused by an allergy or illness.
Also stress is the factor that can cause generalized rash on body.
Viral infection like Additionally diseases such as chicken pox
and rubella can cause a rash but they are usually accompanied by a fever.
If a patient comes to me with such rashes I would take complete history,would have proscribed him antihistamine tablet like Leo cetirizine- 10mg,once a day and see the progress of rash.
In your case you can wait for a day to see the progress of rash,
If it is progressing dont wait just visit the skin specialist as soon as possible.
Hope you satisfied with answer.