I seem to have broken out in red, blotches that itch on my arms and legs. They are not raised and resemble bruises from 1/4 inch to about 1 inch. What could it be? Is it possible to have been bitten by an insect of some kind? It's been about 48 hours since I noticed the first spot.
It would be very difficult to say anything without having a look at the lesions.
What is your age? Are you on any medications currently? This could be due to an allergic reaction to some unknown substance or secondary to insect bite etc or due to heat rash. But nothing can be said with surety without a clinical examination.
You should wash the area and keep it clean, apply calamine lotion at the site and take some oral antihistamine or antiallergic medications like loratadine or cetrizine for your symptoms.
It would be best to consult a skin specialist if the rash does not resolve in a few days. You should get the relevant investigations as advised by your doctor including blood work.
Let us know about what your skin specialist advises and if you have any other doubts.