Hello,
From the picture it looks like a small cyst. It is filled with a soft, whitish brown material that sometimes oozes out onto the skin's surface. This material is called sebum. Treatment includes small surgical opening into the skin and removing the sac (excision biopsy). But recurrence is quite common. I suggest you to get the diagnosis confirmed from a dermatologist after examination.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
It is most likely some kind of cyst. Your family MD sould be able to tell you what it is and treat it. Please do not pick at or poke at it yourself. Even if you are not prone to acne, the back is a sweat and grease producer and can get pores that are blocked with sebum, etc. It's an EZ fix but for a MD to do.