I've been shedding hair & my hair became thinner over all with bald spots at some areas. i've been having some pain in the back of my head in a circle?

See Dermatologist: You should see a board certified Dermatologist. Let him/her examine, find the cause and treat you. The cause could be one of many (from anemia to scalp problems)

Depends on cause...: One's primary care doctor can check for medical causes. If none are found, then one can see a dermatologist, especially one specializing in hair restoration (some treatments: minoxidil, hair transplantation, etc, ...). Medical causes may include: hormonal problems (low thyroid), seborrhea, alopecia areata, stressful illness. Other causes: genetic male/female pattern baldness, telogen effluvium.