What Causes Reddish White Bumps On Legs, Arms And Chest?

I have small reddish white tip bumps that s has came up on my legs and arms and chest..... Then I had a red looking rash under my arms armpit area now it has turned brownish red I ve been putting baby butt cream on it but I don t think it has gotten better...... The reddish bumps with white tip are very itchy