I don't know if this is a general rule .. or if I am just a little over protective, but I have heard that you should not feed your snake anything until it passes something from the last one. Mine I have had good luck with as by the time feeding day rolls around, he has already done his business.

If I were you I would be worried too. If the warm water soaks don't help, I would say make another appointment and see if the vet can do something this time.