I Keep Having Itchy Places Like Bumps And Whelps After

I keep having itchy places like bumps and whelps after I scratch them on my chest neck back stomach and it's worse on my back after I shower looks like some sort of rash and itches, and it's been occurring for about 4-5 days and is sporadic, and then will vanish or leave a red spot after no longer itching and gone, what could it be