What Causes Blood Filled Blisters On The Stretch Mark Of Abdomen?

I recently found like some sort of pimple on my white stretch mark on the upper side of my stomach. And I don t know what it could be? A while back I saw another one much smaller and tried popping it. Blood and a bit of white goo came out. But u can set ill see it. It looks like it hasn t healed properly. Idk what it could be?