Do I have cellulitis or another infection 18 days po tummy tuck? (Photo)

You do not have swelling out of the ordinary, you do not have cellulitis, you do not have abnormal coloring of the scar.

Dear PAVA,  Thanks for submitting your pictures.    From observing the picture, I do not see any signs of infection and the wound is healing well. The coloring appears normal and there does not seem to be separation of the wound. The swelling will improve noticeably in 6-8 weeks. The soreness of the drain site will disappear, once the drain wound heals completely.  There might be other issues like the belly button and the muscles tightening, but you will have to be patient for 2-3 months for final assessment.    All the best,                          Dr Widder

Thank you for your posted question and photographs. It appears that you are in fact healing well after surgery with the redness around your drain sites likely from skin irritation rather than a skin infection.  If you have felt or seen a negative change in your recovery, reach out to your surgeon for an evaluation. Best wishes.