knee joint pain

Question
when i was in elementary school i didn't like running... not until highschool the make us run once a month around the track and around the lake twice a year. i began to like running, have less cramps, less dizzyness over the 2 years. i want to run every other day or something for about... 20 minutes a day? but my knees often feel the pain when i run... any advice? i'm 5'6, 105 pounds... i'm pretty skinny around the joint areas, i drink plenty of milk. i just bought a new pair of shoes maybe that will make a difference?
 do you happen to know much about bone building? like calcium and vitamin d/magnesium intake? and weight lifting, i have this book, saying working with light weights will improve muscles and bone density. i'm only 15, i guess i got lots of time but i'd like to get fit, everyone thinks i'm fit cause i'm "skinny" phuh.
lets see when i run, i start with a walking warm up for like... 10 minutes. then i stretch for a few minutes. then run for 10-20 minutes (endurance? trying to get faster, any tips?), then walk for a few minutes and stretch for cooling down...
  usually i don't get sore doing that, but when i run long distance, my knees start to hurt.. yeah thats all i gotta ask thanks for helping hehe  

Answer
HI MICHELLE
YOU REALLY SHOULD GET A DOCTER TO XRAY THE KNEES TO MAKE CERTAIN YOU HAVE NO ARTHRITIS STARTING IN THEM, YES IT CAN AT A YOUNG AGE BEGIN WITHOUT KNOWING IT.
MY 45 YEAR OLD DAUGHTER POWER WALKS EARLY MORNING 4 MILE WITH TAKES TUMS WITH EXTRA CALCIUM.  U MIGHT WANT TO DO THAT.?  U DEFINATELY NEED LOTS OF CALICUM WHEN USING YOUR JOINTS TO RUN.
POWER WALKING IS MORE IN TO BEGIN WITH THEN TRY AND INCREASE TO THE RUNNING PART.  YOUR BODY WILL BE MORE MUSCLE THAN THIN.  BECAUSE YOUR THIN DOES NOT MEAN YOUR FIT.
YOU NEED TO BUILD MUSCLE MASS TO BE FIT.  YES, LIFTING IS GREAT TO BUILD MUSLCE, REDUCE FAT.  WORK THE DAY OFF IN THE GYM ON WEIGHTS.

WARM REGARDS
PATT
WWW.SCHREKNHAUS.COM