You need a new vet. There is NO reason why he can't palpate (not preferred) or ultrasound (preferred - likely will need a trans-abdominal if she's that far along) now so you are prepared. I don't like to do the blood tests. They are not very accurate. Call the vet again & if he still won't come out, call another. You NEED to know of she's pregnant so you can start feeding properly, she will need pre-foaling vaccines and so you can do foal watch, etc. I highly recommend learning how to test her milk so you don't lose too much sleep, but get a vet out ASAP to start.