Help me! Every time someone says/does something funny I laugh uncontrollably!?

I've had this problem since I was a little toddler who would chuckle loudly and whose parents would receive crazy and interrogating looks. I have gotten in trouble at school and as a server an cantor, many times at church! Like, if someone punches my arm and plays punch buggy, I giggle a lot. It's becoming uncomfortable. One time, a friend was singing in a squeally voice that was so hilarious, I peed my self. There could be complete silence an I'll laugh while reading a book. It will startle everyone and then they think I am going bonkers. I'm not losing my marbles, am I? I just want to be looked at differently. I am an honor roll girl so when I lose my mind over a joke, people don't believe my brains! I've tried that idiotic "count to ten and hold your breath" so I really don't wan that answer. Anyway, Any-who, Long story short, I laugh too much and I need help. By the way, I'm a thirteen yr old girl. Is it hormones? Dos age make a difference?