
If the glands are working as they should, and as suggested (and like with my Frankie) they are not too far back for them to be working properly as each normal stool is passed, they should never need draining manually. And for sure, once messed around with, it can take some time for them to settle down again. I was able to externally drain most of my hounds glands, if and when needed (which wasn't often) but Frankie's AGs I couldn't and didn't like going in to empty them - because of where they were sited.
Fact is, if these glands do become impacted and infected, they need treating with antibiotics, and worse case - even removed which is a surgery to be avoided if possible as it's not nice.
I'd look into fleas if he's suddenly reacting to something back there. If at all possible, avoid the need to manually drain the glands - and they will refill in any case as they shouldn't ever be 'empty'.