Are these old stretch marks or new?
Scrubbing the skin causes blood to rush to the surface, and if the skin is damaged it is more noticeable. When it comes to stretch marks, intentional abrasion stimulates collagen production, and this technique is actually used to treat and heal stretch marks from the deeper layers to the top. (Have you seen the DermaRoller?) However this should be done with proper tools as you don't want to cause more damage.
The redness will go away if you refrain from scrubbing; give it a couple days to calm down.
Congrats on your weight loss!
All the best,
Brittany
It looks like friction rub due to the exfoliation. Wash the areas several times with fresh water. Do not use any cosmetic products at the sites. You can apply some calamine lotion at the rash as it will help in soothing the skin. Also wear cotton clothes. Application of mild corticosteroid cream and oral antiinflammatories like ibuprofen/acetaminophen are also helpful. If the symptoms are severe then it will be best 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 dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.