cat: vomited twice, not eating much, test all fine... help

Hi,

we have an 11 year old male. He's always been in perfect health. a week
ago he vomited up a full stomach's worth of food, cleaned it up, though
possibly it was because I'd switched him to science diet senior
hairball controll (he used to eat this, but a few months ago, he ate
something else because our friends gave us a bag to try; he liked it,
but it smelled bad, and when we bought him his own food they were out
of hairball control, so he eat a whole bag of regular senior food). I
thought maybe the food had irritated him, and wanted him to eat, so I
gave him canned food the next day (wellness); vomited that up as well.
took him to emergency, concerned; they x rayed him because his abdomen
seemed tender; he looked constipated, so they gave him an enema. sent
him home.

he didnt seem to go much from this enema, and he still wasn't really
wanting to eat (canned or dry food); so I took him in for a follow up,
the vet thought he might have an obstruction (there was something
slightly odd looking in the xrays, just a passage that looked possibly
a tad wider than normal), so she scheduled an ultrasound, because he
also seemed have a very slightly odd heartbeat. all his bloodwork, btw,
came back completely normal.

Ultrasound: showed nothing. everything looked completely fine. However,
the vet also said he felt like the thyroid might be slightly enlarged,
and ran tests on his thyroid. ALL WITHIN NORMAL RANGE.

Okay, my problem: the cat still isn't eating very much. He seems a
little lethargic. Normall not a big issue but this cat used to eat a
lot and take, well, pretty big dumps for a cat. He hasn't now for a
week.

If all the blood comes back fine, and xrays show nothing, should I be
concerned?

one more thing, could be totally behavioral: my wife is pregnant. We
started to move around some furniture and put a crib together. On top
of that, the people who live upstairs from us just had a baby. I never
hear that baby, but maybe he can? Maybe he's nervous? He's never even
seen a baby so I don't know why he'd care.

Any thoughts?

I should also say that yeah, it sounds like my vets are grasping at
straws and doing a LOT of tests (we're $900 in already), but they are
the best vets in the bay area, and I pushed them to find a problem.