Hello everyone
My Cat Shadow has been displaying some out of character symptoms

The last few weeks we have noticed him hissing, growling and fighting (if we dont get in there first) or whilst we are out with the youngest Odin

Now Shadow usually comes off worst with scratches to his face and furr all over the place.
We have 5 in total all rescues.
Shadow does not have a problem with the other cats and never used to with Odin

He has however been drinking a lot and weeing a lot and not in the litter tray of late (infact as far away from the litter tray as possible) he is fed the same as the others yet he has gained weight

He has 25g of Natures menu every morning and 25g of Orijen every evening.
He hasnt lost his appetite, and looks healthy enough he is 5 years old, and a twin to Rainbow. He also keeps his distance from the others apart from when him and Odin meet on the stairs. And they also have their meals together but no problems then about 2' apart

Thinking Diabetes

Any ideas before I take him to the vets?
Linda x