Often it's an allergic reaction, but if you have any questions at all, contact your physician.
It could be almost anything and it depends on where they are.
staying in the water too long can be a factor
rash
Chickenpox causes widespread bumps, not clustered. Shingles or poison ivy are just a couple of problems that can cause a cluster of itchy bumps. See your health care provider for definite diagnosis and treatment.
warts
pimples.
Horses get itchy, he is scratching his bottom.
Dysnidrosis
It's a rash.
Irriation from your razor, it could be time for a new one, or better shaving cream, also you could be shaving too much.
you got something. go to the docter
You break out in turnips