Can someone answer this, I would prefer a woman.
I' m not an expert but...
you just put your body through major surgery which can definitely mess up your cycle for a while. I've had this happen simply by traveling!
When blood is dark brown it tends to be "old". I would call your surgeon or PCP if it persists or becomes bright red for advice. If it becomes heavy go to the ER immediately.
Chances are all is well...take care!
having the surgery can mess up your cycle also losing weight quickly will release the extra hormones stored in your fat and will do wonderful things to your cycle , like non stop periods , no periods for months ect, also birth-control pills and other forms of hormonal birth-control can not be trusted , you need to use a second method, like a rubber , diaphragm, have hubbies or boyfriends tubes tyed if you don't want any more kids
your lucky you did not get your period while you had your surgery , you did not need more discomfit
I'll just share my post op experience about this. I had my surgery on Monday and got my period (dark blood to start with) on Wednesday. It was due in about a week and a half. The first several months things were fairly predictable after that, then I started having more not so fun changes with a couple of periods a month, that seemed nonstop! I was tested and everything came back fine. My answer was that it was from the stress of the surgery when I had my period early right after having the surgery. And the changes later were from the rapid weight loss and the hormones released from that. Things have toned way down now that I'm done losing weight, thank goodness. I'd still get in contact with one of your doctors to make sure this is what's happening to you also and not something else.