Stretch marks can appear when there is rapid stretching of the skin. It is common in rapid gaining or losing of weight, pregnancy, puberty, cushings syndrome and overuse of steroids.
Creams containing alpha hydroxyl acids and retin-A are said to be useful in decreasing the stretch marks but the advertised antimarks creams have no proof of effectiveness. Eat healthy, nutritious food ,drink plenty of fluids and do moderate exercises. Laser therapy, and dermabrasion alone or in combination have also been shown to be effective in diminishing the appearance of stretch marks. For that you need to consult a dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Oh I hear you. I have never been overweight either-- in fact, I was always the tall, lanky girl in school. But because of this, my skin wasn't expecting to expand when I filled out during puberty, and I got stretch marks on my hips and butt from it. Years later, they still bug me even though they have lightened. With plenty of research and experimentation, I've made significant improvements. I did this by regular exfoliation and laser treatments. There is hope and with technology these days, they can be improved!
Youtube "Stretch Mark Removal" and you will see plenty of videos showing how this can be done.