I've only just seen this, and reading it makes me wince (and I'm a girl) to think of him in such pain, so I'd have cried at the vets too - so you're not alone on that one.
I think it's positive when the vet said she was frustrated rather than worried.
Fingers crossed his meds will kick in, and she'll be able to get him sorted.
I wasn't into having ours castrated, but as they got older they started to have problems - Dylan with an anal adenoma like elaine.e's Josh (testosterone increases the chances of it coming back), and our Morgan had a secondary tumour in his (both aged around 10/11yrs old at the time).
If he's not going to be 'using' 'em, get rid is my opinion