I also think it's a blckage.
My 13 year old staffy did the same last year, he ate a carrier bag but we didn't find out til it was too late. He couldn't eat or drink and the vet gave us AB's for him which did nothing, they then X-rayed him but nothing showed up, still getting sicker so they booked him for an ultrasound on the Monday but Sunday he passed a little bit of carrier bag then died