I have these dark spots on my butt. I'm 2 weeks post op. It wasn't there at my one week follow up. Is this normal? (photo)

Darkening of brown spots such as freckles and lentigos followed by flaking off over a period of 7-14 days is a normal response. Those spots will fall off on their own, revealing less spotty skin beneath.  You will be happy with this.
No need for alarm, sometimes a mild exfoliating cleanser can help speed the removal of these spots a little.