Dried cranberries are high in sugar. So you have to be careful how many you give them.....they can't have a lot of sugar. Here's a list of foods that are good for them, and the ones you should limit:
https://rabbit.org/suggested-vegetables-and-fruits-for-a-rabbit-diet/
Our rabbit had some issues with cilantro - it hurt his tummy. Some rabbits don't tolerate every thing that is on the approved list. What kind of antibiotics are you giving to him - is that the Sentra? Oh wait, should that read Septra? If it's Septra, that is on an article by a house rabbit society as being safe for treating rabbits. It is sulfamethoxazole trimethoprim but I don't know anything about the dosage. Here's that article:
http://www.allearssac.org/pdf/med.pdf
However, we tried two of our rabbits on this medication and it made them sick, they didn't want to eat or drink, etc.
But this could be a number of things - have you looked at enteritis? Here's an article about that and the treatment they recommend:
http://www.bunnybunch.org/rabbitcare.html#anti
The problem with metoclopromide is that if there is a blockage, the meds could kill them. Do you believe there is a blockage?