Normally I have a light period flow but this time its heavy and clotty and I feel weak. I'm anemic and I heard this was a serious symptom. What to do?

Go to ER. If you are bleeding so much you feel weak, and are already anemic, you should go to the emergency room to get checked out by a doctor. Make sure you let the er staff know that you have a history of anemia, review your symptoms with them, and tell them about your overly heavy periods. They may have you see a gynecologist when you are there.
Go to see your MD. Go to see your doctor for further evaluation. Also need to get some blood work to see if you are anemic and to figure out the cause- which in your case probably related to your heavy bleeding- check your iron level and thyroid level importantly. If your menses continue to be heavy- need to see your gynecologist to evaluate the cause of heavy menses. Good luck.