Pregnant yet fixed

Question
My partner and myself took our 18mo old female cat to be fixed after she had had her first litter.  After placing all the kittens in good homes.  The stiches are out yet she is gaining weight.  Is showing signs of milk production.  Abdoomin has grown.  We think she's pregnent.  Is it possible that the Dr. missed somthing?  I know she hasn't been out of the house since the operation.  

Answer
Eliza,

It is always possible that the vet missed something, but not so much that the queen could become pregnant.  I would take her back to your vet to have her hormones checked and see what is going on.

Please let me know what you find.

Best regards.. Norm.