I've been having trouble getting a full nights sleep. i am constantly waking up in the night. what could it be?

Lots of reasons: Everyone has periods of lighter and deeper sleep; may or may not remember waking up. If you feel fine during the day, you're probably getting enough sleep. If not, try less caffeine, and don't exercise in the evening. Recent evidence suggest that looking at bright electronic screens (phone, etc.) just before going to sleep may interfere. Alcohol also disrupts sleep patterns.

Sometimes the cause: Can be poor sleep hygiene. Retire ; rise same time each day. Keep bedroom dark ; cool ; use only for sex ; sleep. Turn off tv. No naps. Exercise regularly but not in late evening. No caffeine for 6 hrs ; no alcohol or tobacco w/i 2 hrs of sleep. Keep dinner moderate sized ; finish at least 2 to 3 hrs before sleep. Can try warm milk, chamomile tea or melatonin along w light reading or warm bath.