With most meds the body builds a tolerance against them over time. With melatonin there is a similar, though not entirely the same, effect that happens. If you use it regularly there is a risk that your body will either reduce the amount of melatonin it naturally creates, or it will increase the amount of seratonin it creates (which does the exact opposite of what melatonin does) in order to counter the steady spike in levels. I recommend you stop taking it for somewhere around a month - being on summer break should make that easy - and increasing the amount of physical activity you do dueing the day. When you go back on it, don't take it every night. Instead take it every few nights, and stagger it around from week to week. This will keep your body from getting into a rhythm and will delay the coping against the rise in melatonin. Keeping active will increase the amount of melatonin your body naturally creates (as well as increase the amount of feel-good chemicals which ill keep things like depression at bay). If it is noise that keeps you up, try earplugs, or having a radio on to drown out background noise from down the hall. I had to do this when I was in college, because one of my four rooommates sounded like a bear when he snored.

Hope that helps!