3 weeks post tummy tuck and my incision is beginning to separate. Is this ok or should I be concerned? (Photo)

YES!! Seek immediate medical help or return to se your surgeon for follow up care.. Starting of a separation after 3 weeks could be a sign of fat necrosis... 

I am sorry to hear about the complication you are experiencing. Superficial separation of the incision line is a known complication after tummy tuck surgery. Close follow up with your plastic surgeon will be in your best interests; sometimes removal of a exposed suture and/or removal of any unhealthy tissue will expedite healing. Otherwise, wound care regimens will differ from one plastic surgeon to another. Generally, this will involve application of some type of sterile dressing ( in my practice I use a non-stick dressing covered by a sterile dressing). You should have peace of mind that these types of wound healing problems generally go on to heal over the course of the next several weeks, without long-term sequelae. Also important to concentrate on a healthy diet, including good protein source. Occasionally, in the event of a wider scar, scar revision surgery may be helpful down the line. Best wishes.

Thank you very much for sending us your
photograph. It does look as if you have
mild separation of your wound just in the middle. It does look relatively minor at the moment
with no significant surrounding redness (cellulitis).

I think it would be worth keeping a close eye on
the red area around the scar and if it worsens in any way to make an urgent
appointment to see your surgeon.

It is important to have the area dressed regularly
and in our practice we would encourage you to clean the area daily and probably
apply regular Indine dressing. This has
iodine ointment and helps the wound heal.

If you have not seen your plastic surgeon recently
I think it would certainly be worthwhile seeing them or a member of their team
to discuss the best way forward for you.

Best wishes.