Hi Jo
I have a couple of possible causes that these symptoms could be caused by. Excess drinking and eating plus weight loss can be due to diabetes. Another quite common problem in older cats is an overactive thyroid gland. Sure these tests will cost you money but unfortunately without them, you won't be able to get him diagnosed or helped. Treatment is available for both these problems.
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]