Heya,
I am no medical expert, but am a firm believer that for every action there is a reaction, especially where the human body is concerned.
Everybody is different, some womens' bodies take time to readjust after being on contraceptives for long periods of time. Especially considering your body was very young and going through some of the major changes to become sexually mature. I doubt your body had time to get into a cycle properly.
The best piece of advice I could give you is if you don't agree with your first doctor, seek a second opinion. There's no harm in shopping around just to make sure you've covered all possibilities.
However, if your doc isn't concerned, I wouldn't be too upset just yet either. Give your body time to re-adjust.
Peace