I cannot possibly stress the title enough. If you are having overly heavy bleeding that lasts for a prolonged period, and your regular doctor is fobbing you off, GO TO THE EMERGENCY ROOM!

When I was 17, after 5 years of generally regular periods (no worse than any other teen), I suddenly started bleeding heavily, passing large clots, and it didn't stop. It went on for more than three months. I missed so much school that I wound up having to delay my HS graduation by a year. I was bleeding right through a tampon AND filling a pad in an hour. I had no idea where to go, or what to do. I wasn't on any birth control, and was still a virgin, had never even seen a gyno.

Eventually, after weeks and weeks of bleeding, I passed out in the shower. I was rushed to the emergency room, and spent the next two weeks in the hospital recovering from the blood loss. I had 6 pints of blood transfused, and was STILL anemic for months afterwards.
It turned out that I had a particularly bad imbalance of hormones. They treated me with heavy doses of progesterone until the bleeding finally slowed to a stop.
I had to listen to the doctors tell my mother that if I had gone any longer as I was, I would have literally bled to death, because my body was not going to correct it's self, or it would have within the first couple weeks. I kept producing and shedding the uterine lining (just as my hormones were telling me to), faster than my body could handle, taking the blood from other more important functions. I passed out because my brain was being deprived of oxygen, because I didn't have enough red blood cells to carry it, anymore.

The point being, if your doctor isn't taking things seriously, find another one. Don't let it go on for months. If they're telling you the tests can't be scheduled for months, then go to the ER. Once you've been checked in, your insurance will cover the cost of having them done there. When it's this bad, it's no better than being stabbed in the gut and bleeding out from it, and it should be treated accordingly.