What Causes Red Spots And Itching Throughout Body?

I am having itching problems on the whole body since past 8 months . First there is a small red spot,and when u start scratching that area turns red. If I scratch with nails then there are small upheavels. These rashes subside after applying some calamine lotion like dermocalm.Iam a lady who is in 59th year of my life. My weight is 65 kgs. Height is about 5ft. I live in Lucknow in India