Hi!
Please weigh him daily at the same time instead of weekly, take him off any fresh veg for a day and see whether that helps. If yes, please wait with reintroducing fresh food again until the poos have normalised for 24 hours (restart with a little fresh herb) and if necessary top him up with recovery formula or mushed up pellets. His digestion may be disturbed from eating less hay fibre than normal - it makes around 80% of the daily food intake, which you cannot control by eye. Pain in the eye when chewing on the tough grass/hay fibre that is keeping the back teeth ground down evenly may be the cause.
Metacam does not cause any digestive issues, nor should the topical (on the spot) antibiotic in your medicated eye drops because it is not absorbed in the gut. The problem will hopefully right itself once the eye is getting better again but until then, you want to support your boy.
Probiotics and 'poo soup' may also help with supporting the disturbed gut microbiome if your boy is eating too much fresh veg in relation to fibre, which can cause an overgrowth of the wrong kind of bacteria in the gut.
Please contact your vet if problems persist.
Information on how you can improvise on feeding support in a pinch as well as support products (recovery formula, probiotics etc.) in this guide here:
Emergency, Crisis and Bridging Care until a Vet Appointment
Digestive Disorders: Diarrhea - Bloat - GI Stasis (No Gut Movement) And Not Eating