How Long Does Broken Leg Take Time To Heel?

I am in the 9th grade and i had knee surgery ladt year- i broke my leg and tore my minescus. I dont remember the name of the surgery but i do know that there is now a nail somewhere in my knee. This year i tried out for my high school basketball team and made it. My basketball coach is a also a physical therapist, so she noticed the brace i was wearing, checked out my knee and told me i should go back to see the orthopedic surgeon. After she finally convinced me to go, he told me I couldn't play, and that i had to wait a few more months for it to heal. So all i really want to know is why isnt my knee better yet, what is taking so long for it to get better, and what can i do to speed up the healing process? Another thing is i had to get an MRArthrogram of my knee to see if they could find that problem, the next day my knee was bleeding black from the place where they injected the dye, is this bad? Should i be worried?