It hurts if i try to lift something or straighten the arm out , the area is tender to touch also.

More info needed: In What part of the arm is the discomfort located? If it's the shoulder or elbow joints and there is no history of recent injury, inflammation like tendonitis would be suspected. This responds to rest, cold and/or warm applications, rubbing with liniment like Ben Gay and, if you can take them, anti-inflammatory medications like Advil or Aleve should help. If symptoms persist see your physician.