Hello. I'm very weird about talking about haha... 'body parts' but since I'm typing online I guess it doesn't really matter.
A red bump the size of a grain of rice really wouldn't concern me too much. I would (from your description) attribute it to a bug bite or a pimple before saying it's an infection. Technically I would say it would be INFECTED from the dog scratching at it or something, but calling the bump it's self an infection is weird. I would put a an anti-biotic cream on it but I have no idea what is available in your country. If you can research and see if you have plain Neosporin like the kind humans use you can use that on animals. I would highly advise you to check every single ingredient in it where you are before using it incase it's different then what I have in the USA.
As for the yellow goop on the fur, I can tell you this is VERY common in dogs, mostly those who are not neutered
I work in a spay/neuter clinic and hate to say I've seen plenty of dog and cats private parts and what you are describing is very very very common for male dogs of sexual maturity... and even some puppies!
I would not put it as a 'cold' because it's most certainly not in any way shape or form. Maybe an infection but that's a totally different thing then a 'cold'.
I have no experience with Norfloxacin so I google searched it and it appears to be a fairly dangerous drug and just from what I read, if it were my dog I would immediately stop using it.
Norfloxacin is a synthetic chemotherapeutic agent occasionally used to treat common as well as complicated urinary tract infections. It is sold under various brand names with the most common being Noroxin.
I really can't find much information on it in veterinary use. It barely looks legal in the US. It is used to treat SEVERE infections in humans. I mean, this is just from searching around online so you really want to do your own research too.
He could very well have an infection, but there are so many safer drugs then whatever that is that you were given. Clavamox seems widely available and would be great if you could find that.
Good luck... I'd really get a second opinion. I have no idea what kind of degrees they have to have in China but I'd ask about that.