That can be normal. Sometimes it takes a while for things to straighten out when you first start. You can also skip periods too. I wouldn't worry too much yet. IF it's still going on for a week or so, maybe just try going to the dr. I was put on birth control at 14 to regulate my periods. Every girl is different. If you're not bleeding real heavy I wouldn't worry about it at all.
this is not normal i would tell see the doctor it is weakness to have long periods that means iron deficiency talk to your doctor bcoz you are too young. hope this help you