Aw. sorry to hear this but your vet suspects a URI and the Baytril will help.
Bit baffled as to why he gave you Metacam as it is a pain relief medication - mine never had it with antibiotics for URI's only UTI's.
Right - what dosage have you been given for your boy ? Baytril can be harsh on their little tums so would advise giving a probiotic around 2 hours after the Baytril. This will help maintain his gut flora and help prevent any soft poos.
Fibreplex is great and available from any veterinary practise for around £8.
http://www.vetuk.co.uk/rabbit-suppl...ibreplex-for-rabbits-and-small-rodents-p-1180
Any signs of diarrhoea, stop the Baytril and contact your vet - this is very important.
Make sure your boy eats well too, Baytril again may reduce his appetite so of you can weigh him every couple of days or so and keep a record. I know it is hard when they are not well and don't want to be messed around with but I have always weighed mine the same time as they've had their meds.
Have you tried a dust free hay ? Is he on any kind of shavings that may have irritated his respiratory tract...fleece blankets/vet bedding is very good for them and reduces the risk of URI's drastically I think.
Keep us informed of things - many of us have had piggies on Baytril and can help with any worries you have

Hope little one picks up very soon, will take a few days for the antibiotics to work into his system before he shows any signs of improvement.
Keep a close eye on him and keep him warm and dry as piggies can go downhill very quickly
