Please help my shoulders..

So this has been going on with me since mid 2008. I keep picking at the pores i see on my shoulders, after being on a drug to help clear up my acne. I didn't understand why I did this and today I decided to actually google this to see if it's common, and here i find it's a real problem. I thought back to when i was younger and realized that when i was 6 I used to pick at my legs, and when i was 12 i started picking at my head, so much so it was always red and painful. It stopped when i got to high school but after clearing up my acne it's started again with my shoulders. I don't know what to do. Summer is coming up and it's getting to the point where I can't bring myself to wear a T-Shirt because the top of my arms are red. I would love to be able to wear sleevless dresses and singlet tops this summer, but i don't know how to stop picking, and even my parents wonder why i don't swim in the pool on a hot day, again it's because i dont want anyone to see my shoulders. I try painting my nails to stop picking or even cutting them down real far but it never works for more than 2 days. Please can someone help me with what to do?