What Causes A Cluster Of Blisters Under The Skin?

hello i have tiny dots on my side, i have had them about 3 years as far as i can remember the tiny black dots are not alone they are in clusters .like a bunch of 15 of them here and a bunch of 20 over there. their texture is as that of a scab. They are very tiny and are under the skin.... I would like to know what they are and how to get rid of them