How do we know the tumor is still there? A PET scan will show scar tissue very similar to cancer tumor for months. If you (he) detects a lump that in itself also is not necessarily anything. The body takes time to heal and get rid of bad tissue bit by bit. The radiation doesn't make the tumor magically disappear, it merely kills the cancer cells. I know he is anxious and certainly anything not right seems like the worst case may be possible, but chances are it is all part of healing. The surgeon seems to not be alarmed if the schedule is for three weeks out. I know the time seems forever. I can pretty much guarantee for the next several years anything that feels out of sorts will be cause for sleepless nights and will later prove to be nothing at all, or at least we hope that's the case. Please try to reassure your husband that it will most likely be alright, that he is healing, and perhaps some birthday cake might be needed for this second chance at life.
Bless you for looking out for him. That makes you an angel on earth just like my wife. I know I wouldn't be here if not for her.