Thank you for your question.
I am not a medical professional and would not be able to give you medical advice. It is also impossible to say with any certainty what could be causing this rash. I would suggest contacting your doctor and if necessary, a dermatologist. However, in the meantime, here are some possible causes:
Allergic reaction. You could have an allergic reaction to a food you have eaten. Allergic reactions can appear even if you have eaten the food before and not had a reaction.
Bed bugs. Bed bugs can't always be detected by looking at your bed as they are quite small. Adult bed bugs are less than one-fourth inch, with the immature bugs as small as a pinhead. They are light in color so often blend in with your bed. Bed bugs can be found in couches, cluttered blothing, suitcases and even on pets.
Flea bites. These also start wwith small red bumps and can appear as a rash and are extremely itchy. They can hide in your pets and they can live in small cracks on your floor. With flea bites, if you press down on the rash, it turns white.
Mite bites. Mite bits also are small red bumps that look like a rash. You usually don't notice them until you notice the itching. With mite bites, the skin surrounding the bite usually hardens.
Scabies (a type of mite). Scabies looks like small red pimples clustered together to form a rash-like area. They are extremely itchy. They are usually found on the folds or bends of the skin, such as behind your knees and in between your fingers.
Poison ivy or allergic reaction to a plant. While poison ivy doesn't spread, if you scratch it and then scratch somewhere else on your body you can bring the rash from place to place.
I hope this helps.