I change moods everyday, i start off being happy then i get really sad and sometimes i cry? what can i do?

everyday i wake up and feel really grumpy(well yes who doesn't) then i will be happy but then later in the day i get really upset, and i cry, i like to be alone during that time. and this happens to me EVERYDAY. i have thought maybe it could be bipolar or something like that, but i don't know what to say or how to say anything about it to my parents so they can take me to a doctor. i really dont like the times when im sad but i cant seem to get rid of the sad times...