Your young, I doubt you'll get stretch marks. People get stretch marks when they loose weight without exercise.
Everytime you rip a muscle, the body releases a huge amount of white blood cells that clean up your whole body.
No bread(no yeast).
Start drinking lemon(not lime) & water, it will help you get over the crave for sugar.
Plyometrics(excellent for losing weight):
I do all bodyweight workouts. I've been Injury free for a very long time.
Look into doing push-ups(lots of variations)(triceps/chest/shoulders), chair dips(triceps), chest dips(chest), hip bridge(hamstrings/glutes), squats(quads, calves), chin ups(biceps), pull ups(back), reverse crunches(abdominals/posture muscles).
They will be hard at first, but as you get use to it, your body will get stronger and stronger.