Stretch marks on top of old stretch marks?

I finally reached the 29 week mark as of today. My belly has itched on and off for about a couple of weeks now. I was really looking at my belly today and I noticed that my old stretch marks are becoming red. Not all just a few areas and no new ones have formed. Is it possible to have new stretch marks right on top of the old ones? Or is it the old ones becoming irritated and becoming red because of me itching them?