Bleeding very heavy after taking provera (medroxyprogesterone) 10mg for 10 days, prior I have been bleeding for 3 months I'm worried about too much blood loss?

Have blood test. This is a normal effect of prover to induce the full thickness sloughing of your lining. Check your blood count checked to see if you are anemic from the bleeding. Go ahead and take some iron.
Get checked. If you are feeling light headed and tired and your heart is pounding you might need to go to the er to get checked for very let blood count. You might need a blood transfusion. Going through a pad every hour or less is considered heavy bleeding. If you are feeling ok call your doctor in the morning. Your doctor might want to see you and check your blood count.