How to reduce appearance of stretch marks?

I am 18 years old 5'1" and 97 lbs. I am very small and petite. I have had these stretch marks ever since I can remember though, probably since I was 13. They are the white stretch marks, not red. I've tried Palmer's coca er but I've only used it for 3 weeks. The instructions say use for 3 months. I just recently purchased Avon's stretch mark cream. Any ideas..? Does anyone else have this problem?