My 2 year old had two small black dots on his elbow about 3 weeks ago. Those have faded, but now he has hives, swelling and itching in that area. Going on two weeks now. Have treated with Benadryl cream. No new foods or detergents have been introduced. Nothing seems to make the hives disappear.
You need to meet a pediatric specialist and a skin specialist for the same. They will assess your child and surely help you with your queries.