I can't stand up straight 3 weeks post op Tummy Tuck. Is this normal?

i have never seen an abdominoplasty patient who did not stand up straight eventually. sounds like you had a very agggressive surgeon which should give you a nice reult. be patient

If you're concerned, I would go back to your plastic surgeon as you should most likely be able to stand up at this point.

Congratulations on your recent surgery.  Its important at this stage of your recovery to follow your surgeons post operative guidelines and be patient. Mobility tends to improve daily and most can stand upright at this stage but each patients recovery is individual. If you are concerned you should arrange a review with your surgeon.

This can absolutely be normal.  Be sure you are following your surgeon's advice.  This may include moisturizing and/or massaging your abdominal scars to soften them.  Typically the "standing straight up" posture comes around 2-3 weeks, with improvement each day.  If you are concerned about complications, be sure to ask your surgeon.