I don't know what I should do.?

I am sixteen years old and I got stretch marks a year ago. I have them on my arms, thighs, back of my knees, and alittle infront of my knees. Then last summer, I had fleas all over my house because of the dog and I have scars on my legs from scratching them. It keeps me doing alot of things that I want. I always wear jeans and sweaters to cover up my body because I don't want anyone saying anything or looking at me. I can't go swimming, wear shorts, camis, anything. There's no way I could get rid of them. I'm not overweight. I guess I got them from growing too fast. But, I don't understaand why I have them behind my knees and on my arms. I am not confident at all. I see other girls who don't have any problems and it bothers me so much. I was in track and play soccer so I don't understand. Can anyone tell me what to do?