Hi S.,
I agree with the other ladies about you could have possibly had a miscarriage. Also, have you had any sharp pain on one side. Ovarian cysts can burst and create heavy bleeding that last for a while. But, generally there is a good amount of pain with those.
I know that you have said that you have been stressed, but honestly you have to be under an enormous amount of stress for it to really change your periods like you are describing. I was talking with my OB one time about this, and she said that stressing over life changes (buying a new house, changing jobs, financial issues, etc.) isn't typically enough to change your periods.
I agree that the right thing to do is make an appointment. Honestly, I really surprised that your doctor didn't want to examine you before they prescribed the meds. It seems stange to me that he/she just assumed that it was a horomonal issue affecting your period, especially when that has never happened to you before.
The best of luck to you. I hope you get feeling better very soon!