Does masturbation cause stretch marks? I noticed that my thighs are little itchy after masturbation

I'm 17 years old and I start masturbating since I was in grade school, but I kept it a secret hehe. I just noticed recently that after masturbating my thighs was little itchy and then in the morning I took a shower and noticed I have stretch marks in my outer thighs and it's color red and I feel depress I want to get rid it without doing any treatment. But I think I got stretch because I'm gaining weight and I'm stress in online school. :<