Late period

Ashlyn
My period was projected to be on the 10th and 4 days after that. But I havent had it since the 10th and my projection date keeps getting pushed farther and farther back. Im a little scared to take a test because I dont want to be disappointed ! Any advice. What do you guys think is going on. I mean im 19 and idk if I just have a longer cycle. HELP!