Wow, this sounds like Leonidas before the big snip.  Is it possible
there is a female around and she's in heat?  That was Leonidas' thing.
He still does it when the little hussy comes around (apparently she
wants blue eyed babies).

Have there been any changes in your household?  New furniture, someone
not there, anything like that?

Perhaps a vet visit might be in order, since it is a behavio(u)ral
change.  You have my sympathy about the crying all night thing.  I
guess there are advantages to not sleeping more than two or three hours
(even if I'm too tired to think of what they may be).

Smokie Darling (Annie)

Vet should see him, could be hyperthroidism which is treatable.  Norm

--
"The web has got me caught.  I'd rather have the blues than what I've
got."  <via Nat King Cole>

There are just so many things that you need a vet to look for.  A bad tooth,
Something in an ear,  etc.  At least a vet visit would give you some peace
of mind.

Jo

There could be a ton of things that could be wrong, but i wouldn't
immediately run off to the vet just yet.

How old is your boy?  Is he neutered?  Indoor/outdoor?

Check all of his limbs...  Is he limping in any way?  Does he whine
when you touch his paws?  Try checking the pads and between his toes.
Don't forget to check the tail too.

I'm assuming there's no obvious facial signs, like discharge from the
eyes, ears, or nose, or rear?

When you hold him, does he yowl when you compress his sides?  Try
petting him and running your hands along both sides and see how he
reacts.  Do you feel anything possibly abnormal (careful, cause I've
had clients say that they've felt big bulges on their cat, and it
turned out the cat is just obese)

When he yowls, is he doing anything in particular, like jumping, or
being by the window?  Meaning is there any event that could be
associated with the yowling?  Maybe a time of day?  You said the
litterbox was normal, but have you seen him go to see if he's straining
or having difficulty?

All of the above is what a vet tech or vet would do if your brought
them in.  They would ask you questions about his lifestyle, eating
habits and behavior and then perform a physical exam to see if they can
identify if the sounds are coming as a result from pain and if so try
to localize what is causing pain.

Also it could be just an odd fluke thing.  I cant tell you how many
people have come in because their pet is acting all off, and when they
come into the clinic they are acting just fine and we don't find a
thing wrong with them.

Like I said, the above questions is what I, as a vet tech, would do if
the cat was in front of me, and that's normally what a vet would do
too.  I'd try to wait another day and observe him like a hawk and see
if you can learn anything else.

The more the vet knows, then the more they can narrow down what is
wrong or not wrong.  Coming in and saying "My cat is agitated and going
nuts" isn't too specific. Besides, it could save you money and a trip
to the vet.

That's my advice, hope it helps

Kristi

You say he's a 'little boy'. Could he be entering puberty and longing
for female company to do what his hormones are suggesting? Either that
or maybe he's lonely and wants a playmate? Purrs for him to feel more
at rest soon!

Lots of purrs and best wishes for nothing serious to be wrong with Oliver,