It seems that she probably experienced a split season. Usually when this happens, the bitch comes out of season before ovulating and then comes back in and ovulates very soon after coming back in. If you didn't do progesterone testing up until the point where you got an 'ovulation confirmed' result, then you wouldn't know she has come out of season - if you just went on the rising levels. Then you bred her just before she came out of season and before she ovulated.
> I learned how to and performed cytology on the bitch when with the stud dog to make sure we had the bitch properly covered and I'm pretty confident we got the timing part perfect.
Cytology is really quite difficult to read properly, and needs a lot of experience. Whilst it is not difficult to take the swabs and make the slides, interpreting the results really needs and experienced and I just doubt you could be doing this accurately by yourself on your first bitch....
> Another few days later we had a lighter white discharge which again had no smell, the vet this time said we should put the bitch on an antibiotic just in case it was a minor infection. The antibiotics seemed to clear it all up without any problem.
Odourless white or creamy discharge after breeding is very normal and not a reason to put a dog on ABs. The discharge clears up by itself, so likely that had nothing to do with the ABs. Please don't overuse antibiotics - they have many adverse effects, from affecting the immune system of puppies, resulting in larger than usual puppies, resulting in antibiotic resistance so that when you really do need them, they are not as effective... and so on.
>Now that my bitch has gone back in season straight away do I breed her again now from this season or do I wait until the next one?
It depends on when you want puppies. No reason to breed her again, but if you want puppies soon, then do so. However you might not have long to wait because she may well be over already by now - she is likely not going to be the usual 10-12 days before being ready now, she is likely to ovulate very soon after coming back in again, that's what happens with split seasons. They are not 2 separate seasons, it is one season interrupted....
>the advice I have been given so far after the first pregnancy was confirmed as a failure was that it was very important to make sure I breed my bitch again on the very next season. I was told that if a bitch has a failed or false pregnancy or even recovers from a treated pyo it was essential to breed them on the very next season as repeated unproductive phantom or false pregnancies can cause the lining of the uterus to thicken each time which is the prime cause of cysts to develop causing uterine infections and ultimately pyometra.
I'm not sure who gave you this advice, but the only reason to breed her again immediately would be if she had pyo-ed. Which she hasn't. If she had pyo-ed she is likely to do it again after her next season, if not bred. So breeders need to breed ASAP and then spay before that can happen. But if she has just missed a pregnancy or failed to get pregnant or had a phantom, those are in no way a reason to breed again immediately. None of those things are going to cause cysts or cause her uterus to thicken. The uterus of a dog is constantly degrading over the dog's life time and the more cycles the dog has, typically the more degraded it will become - but those issues don't cause anything more than the usual process.