Hi. i'm 16, and today i started my period. i normally have heavy flow the first day, but this time it is very thin and watery. i'm really scared.

Change in cycle flow: If you are not sexually active, I wouldn't worry. If nothing else in your health has changed, it could be stress or most likely nothing. If the flow for the whole cycle is different, wait a couple more cycles to see what is going on. Often, you can have slight change like that with your period every now and then. If the pattern has changed after 3 periods, you can see your doctor.