Maybe the xray is the way to go. I know it can be expensive though. We pay around 200.00 here for 2 views. But it could be an obstruction and if it's a hairball putting Fister on fluids will help get it moving through his system- this happened to our cat once- the vet was sure it was a mass because it was the size of a fist and even suggested that Sneakers may not survive the night (she had stopped eating and drinking and was hypothermic- but she was just there overnight on IV fluids that had some antibiotics in them as well for good measure and the mass which turned out to be a hairball started moving again and she was eating on her own the next morning.

The xray might also show if it's IBD or something else. Just thinking with the weekend coming up, it might get more expensive if you have to get him help on a Saturday or Sunday. If they could get him on some fluids that would be good too either by drip or sub-q injection to help him along. Hoping that things turn around for him soon.