If he has a discharge, then a swab should be taken and sent off to see which antibiotic is needed for his URI.
I do think he needs to be seen, as re-occuring URIs are a sign of heart problems. Saying that, it could be a range of things. Have a look at my thread on Buttercup -
http://www.guineapigcages.com/forum/...al-thread.html . She has had 2 URIs, then I caught her wheezing last week and this I believe was the beginning of another URI. The top part of my post you should have a squiz at, it may help you.