Hi
I would always want to get a cat with these symptoms checked out by a vet in case there is a serious problem. Its not possible to know what is causing him to be grumpy but pain will certainly do that to a cat. Weight loss is also a significant and worrying symptom. I hope nothing bad is happening but I can't reassure you.
Cathy Wickenden BVet Med MRCVS
Barton Lodge Veterinary Centre
1 Midland Road, Hemel Hempstead, Hertfordshire, HP2 5BH
Tel: 01442 216048 24 hours
[
www.bartonlodgevets.co.uk]