I have a lump in my back what could it be?

Many possibilities. A "lump in my back" can be due to a number of things including a lipoma (fatty mass), sebaceous cyst, lymphoma, tumor (muscle, skin, or other tumor), keloid, bony prominence, or other causes. See your doctor for a more definite diagnosis and possible treatment plan.
Remove new lumps. New lumps on the back may be surface growths or dermal (under the epidermis of the skin but above the fat) such as cysts, keratoses, moles, fatty growths (lipomas) or muscular growths. There truly are a myriad of possibilities. Either a dermatologist, surgeon, or your primary care doctor should examine you but in order to prove it's not malignant it is wise to remove new lesions for a biopsy.