How can I treat severe stretch marks?

stretch marks around armpit, back arm, thigh, back leg, hips, knees, waist...i am just 21.. Have never gone over weight. 5'8 and have been just 65-76 kgs...and the stretch marks are white, thick...i have been using cosmo stretch mark cream from 4 weeks...seen no difference...just want to get rid of stretch marks specially the ones on arms...:/

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