My doctor told me that birth control pills contain small amounts of estrogen and progesterone, and these hormones prevent me from ovulating. i assume that it has something to do with the levels of the gonadotropins that i asked about earlier. can you explain this to me?

Ok... This is a bit complicated but bear with me. In a female's body Estrogen and Progesterone are two of the major used to maintain the menstruation cycle. Gonadotrophic substances are an entirely different topic with it being the hormones FSH and LH (These hormones are released while an egg is in development in the ovaries). 

Without going into even deeper specifics. Estrogen is used by the body signal to ovulate, as well as thicken the uterine walls... Progesterone is used to maintain the uterine walls "after" the egg is fertilized. What the pill is suppose to do is actually force a premature ovulation, which is why there is estrogen. The Progesterone's job as is maintain the uterine wall's endometrium to a low level and helps keep blood loss from a period at a minimum. 

If you need clarification please feel free to question.