Welcome to healthcare magic
From your description it looks like you are having stretch marks
. Gain or loss of weight can cause stretch marks and thigh is a common site or it.
You may apply a thick moisturizing cream and massage
over the stretch marks twice a day so that they become less prominent. You may use Palmers massage cream for stretch marks or Venussia max cream.
Procedures like derma rollers, fraxel
lasers etc will also work to make it look better. You may consult a dermatologist
practicing cosmetology for the same and these procedures will be costly.
Hope this helped