I have had a spot of itchy bumps on my back. it started as small humps, turned into welts, now they're back to bumps with black spots in the center. what could it be?

Back rash: If the eruption is only one.side of your back, is in a line distribution,and especially if it was preceded by a dull ache for several days it could be a shingles infection( herpes zoster). Otherwise, insect bites or an allergic reaction are possibilities. I recommend consulting your physician or a dermatologist for diagnosis and treatment. If it's shingles, it's important to get early treatment.