Thanks for writing to us.
It seems that you have an infected sebaceous cyst
on your shoulder. A direct examination of the area is an integral part of diagnosis. Systemic antibiotics and surgical removal might be needed depending on the size.
I hope this information has been both informative and helpful for you. You can consult me again directly through my profile URL http://bit.ly/Dr-Praveen-Tayal
Dr. Praveen Tayal