One very likely possibility is that you are dealing with a case of hives
(also known as urticaria). Hives are an allergic reaction in the skin. There are many different things that can provoke an attack of hives. For example, if you are allergic to something like mold, pollen, pet
dander, or chemicals and you are exposed to it, this may provoke hives. Hives can also occur sometimes because of stress, or they may be provoked by a viral infection or other common illness.
The first thing to make sure of is that the hives are not part of a more serious allergy reaction. In particular, if you notice any swelling around your eyes or of your lips and tongue, or if you have any wheezing or trouble breathing, then these are likely symptoms of a serious reaction, and you need to seek emergency medical attention.
On the other hand, if you are just experiencing these intermittent blotchy areas without other symptoms, then you can see your primary care doctor
at your earliest convenience. They can confirm the diagnosis of hives and also suggest which type of medication you might take to help relieve the symptoms.
I hope you feel better soon!