look into prophetic dreaming. two theories as to why this occurs, one is you're psychic and are picking up on future events. more logically your subconscious has worked out through subtle cues in your waking life events that will occur and is warning/telling you about these events in your dreams.
i'd keep a dream diary and interpret your dreams, it could help you figure out when these things will occure, as well as help you control your dreams. some people [so i've been told, i've never been able to] can tell themselves what to dream about. you could also try things like write down the foods you eat before bed, certain foods can effect ones dreams [dairy for instance, i eat cheese i have horrible nightmares, a friend of mind eats cheese and has vivid dreams] smell is another one, peppermint and orange are the two that effect dreams the most. experiment to see if there's a trigger for your prophetic dreams.
daily meditation could also help you. again, keep a journal and write down things like date, time, length of session, and anything that you might of saw/heard/sensed. ask yourself a question, something simple but uncommon like 'will there be a quiz in math' or 'will my friend be late for class'. see if you get anything, like a vision, then write it down, at the end of the day, mark down what came true. this could help you with control as well as determining your ability. final option, balance all your chakra's, if energy is pooling in one [probably your third eye chakra] this could be causing all the prophetic dreams.