Are there any vets or animal experts on HB?

This post is probably going to be animal TMI but I am so worried!

My cat has a history of needing his anal glands expressed, this hasn't been such a big deal, I take him into the vet and they do it and then we go home.

The other night he started hissing at his butt and so I thought it was probably time to take him in and have them expressed. Sure enough, they were full but the tech said everything looked normal.

Usually after I take him in we go home and he's fine until the next time (months!) we need to go back in. However, I noticed that even after we got home he would go to clean his penis/anus and he would kind of growl and hiss at it.

This morning after I got to work my husband called and told me that he was again, hissing at his junk and then proceeded to pee on the leather chair in our living room. This is SOOO out of the ordinary for my cat. He has never pee'd or poo'd outside his litter box. EVER.

My husband also said that after he cleaned it up he was just checking Nat out and noticed that it looked like his bum had sores on it, little open wounds (maybe from cleaning too much because of irritation??). Those sore were not there when I took him to the vet a few days ago and I don't remember seeing them there yesterday either.

Anyway, I've made an appointment with his vet but it's not until I get off work (I can't take the time off) and I'm just really worried about him.