I am having itching on my back side of joints(underarms, behind knees , butts, groin area,elbow area , ankles and area between knee to ankle) itching increses during colder days and during sleep time when body is hotter. It feels like something is biting from inside .there is no physical appearance on skin at  all other than itching scars so doctor cant figure it out too..This is from last 2 years or so. Tried every thing even dermotology med too but no solution. It starts bleeding due to excessive itching. What is it ? I need help plz