You stated that you had your gallbladder
surgery 3 weeks ago.
I am assuming this was done through a laparoscopic approach.
Occasionally, during surgery, due to manipulation of the bile
duct, the channel that carries the bile from the gallbladder into
the intestine, a small stone can escape and plug the duct. If
this happens, you will have lot of pain, fever,nausea, vomiting
and even yellow jaundice
. You don't seem to have those symptoms.
The other possibility is a inflammation of the pancreas
since it is
in close proximity to the gallbladder. I have a feeling that your
symptoms of pain under the rib cage and radiation
to the back
is suggestive of "Pancreatitis" , may be a mild case. You should
talk to the surgeon who performed your surgery and ask him
to send you for some blood tests for pancreas, like Serum Amylase,
Serum Lipase, Blood count and also a repeat liver enzyme tests.
This might give some answers to your concerns.
Wish you good luck.