I think that you should be able to apply for renewing your visa at US Embassy when you still have valid visa for 2/3 months. The consular officer might ask you the reason/ documentations for additional visa since the embassy might have already issued you the visa good enough to complete your bachelor or master degree. You can contact directly to US Embassy at Kathmandu at consktm@state.gov and ask your questions. You will be responded within 1 or 2 days. Good luck