I get an itchy back frequently with pink/red spots like unraised pimples. what is this how to fix?

Possibly a reactive: This could be allergic reaction or contact irritation. you may need to find the cause for it or be evaluated for allergies with allergy testing. If related to contact irritation allergy testing may not be helpful. History and good journal keeping may be essential to discover the cause and strictly avoid it.

Check shampoo: The localized nature of this suggests a contact allergic outbreak.We often have a stream of shampoo suds coming down the back.Some shampoos have chemicals that can do this.If you take a few drops of suds and place it on the pad of a Band Aid,you can apply this to normal skin overnight and see if it breaks you out.If not, it's not the culprit, and you can try other things until you find it.

Urticaria : Studies show people with allergies and hypersensitivity can develop hives on their back in response to an allergen , possibly in your detergent, possibly in the environment. I advise allergy testing and a full medical exam with your physician. Take a pregnancy test and try Benadryl, an over the counter antihistamine, to try to alleviate your itching and apply 1% hydrocortisone. Good luck.