I'm on my third week of my period and it heavy and there are
Clots. Everyone been telling me that as long as the clots
Aren't as big as my hands there nothing to worry about. It feels
Like I have lost so much blood that at times I feel dizzy and very
Sick to my stomach

You should go see a doctor.

The doctor is really your only option. A period for 3 weeks isn't normal. This needs to be checked out. You won't get a diagnosis on the internet, not even from a doctor. The only way to find out what's going on is to go in to your doctor.

Guesses won't help you, and that's all we can offer. That's all anyone on the internet can offer, and there are 100's of guesses based on your symptoms.

See your doctor asap.