Confused dog health issue

Question
"Hello,
this is a strange story but try to bear with it, its important to me. for a couple of weeks my pekingese was trying to get out of the house, whining, and just trying to leave. he is not neutered and so we think a female from our neighborhood must have been in heat. over these past couple of weeks, he refused to really eat anything, but was still drinking just fine. we even had to try to just force him. so then off to the vet, who took a regular blood test, fecal test for parasites and such, and an xray. the xray revealed his liver was a little small. according to the vet, the blood work didnt show any problems and he figured i should get an ultrasound to see what the issue was by an internist which costs too much money. i told him about the female in heat issue and he didnt think the lack of appetite was related to it. but a few days after he stopped trying to get out of the house (i guess the female was no longer in heat) he started eating again. this patten of normal eating continued on for a couple more months after the "female in heat" incident. he would even bark and demand to get food. he would eat a lot. but for the past couple of days hes been eating but a lot less of an appetite. doesnt bark and sometimes have to try and motivate him to eat something. sometimes he circles around the plate and tries to head butt it and then not eat. but sometimes he will eat a little after head butting it.

my vet initially thought he might have a liver shunt but i guess the normal blood test revealed that "nothing was wrong." we didnt take him to the internist for an ultrasound not only because it was too darn expensive, but also because he started eating normally again, but sometimes not as well. my main concern really is that i read somewhere that headbutting can be a liver issue or liver shunt. also, just the fact that he said that the liver was a little bit small really concerns me whether or not the blood test came back normal. should i be right to worry even though he doesnt show any real extreme liver disease symptoms except for the lack of appetite at times, and head pressing the food? should i worry about the small liver on the xray even though my vets blood test revealed "nothing wrong with the liver or anything else"?

im sorry but i have had bad experiences with vets and am extremely skeptical of their judgment. i feel like even if i pay them a million dollars, they still wont come to any real conclusions and help me, and ill just end up with a sick dog and penniless in the end. i dont know what to do so please help me, tell me if im worrying over nothing?

thanks,
karmen""

Answer
Your vet has made some kind of tentative diagnosis and wants you to confirm it with other tests.  Of course, it is ultimately your decision and if the dog has recovered, you do not have to make that decision immediately.  With a liver shunt (rare in the Pekingese) the blood ammonia level will increase after a meal, and that can be tested.  Also, if there is liver disease, the vet can test something called serum bile acids before and after a meal.  If these are normal, then having a small liver may be OK for this dog.