Tummy Tuck 6 wks ago, last 2 wks I've noticed dark red stretch marks appearing. hy do I have these, and will they ever go away?

I have never seen a stretch mark caused by an abdominoplasty.  Many are removed when they are below the navel and some might be moved somewhat, but never created (in my experience).  There is no non-surgical treatment for stretch marks so don't waste your money.

It is very unusual that you are forming stretch marks from surgery.
It is more likely that you are visualizing pre existing striae that become more visible from increased blood supply during the healing process.