Hi there,
Definitely make that appointment to see your gynecologist! Your period sounds abnormal and you may have too heavy of uterine lining which is causing you to double-menstruate. They'll be able to give you an ultrasound to make a final determination if that's the case. Keep tracking your periods religiously because your doctor will want to know exactly how long this has been going on and all the details behind it.
You should see your gp. If your bleeding heavily you can become anemic so watch out for dizziness and fatigue, if this happens go to a clinic sooner. It may be nothing but it's abnormal and should be looked at.