As you are getting full erection during masturbation, you do not have serious problem. Because you go home every 2 months, you are under the pressure to perform. This performance pressure is the root cause of your problem. With every failure, your pressure is going to increase and your problem is worsening. Do not worry and be apprehensive about your performance, just relax yourself. Do not try to perform for initial day or two. This will reduce your pressure. You may take medicines to get erection under medical supervision for a week or so, few successful acts (even with the help of medicines will boost your confidence). Watching porn movies cannot lead to this problem.