sneezing chickens

[dormerroof]

I'm new to this website and chicken keeping. I bought 7 pol hens who had been vaccinated against 5 illnesses including mycoplasma and salmonella tested. They were all fit, well and laying. I bought a further 5 hens from the same supplier and naively mixed them together straight away thinking they were also fit and well because of they were from the same supplier and vaccinated against the same illnesses. Unfortunately, all my flock came down with sneezing and discharge. My local vet diagnosed mycoplasma, I told him that they had all been vaccinated against it, he told me you can't vaccinate for it, who is right? He gave me terramycin, it didn't work, one of the hens had bubbling eyes, he gave me a 10 day course of Baytril, it came with a 38 day egg withdrawal (10 while on medication and 28 after) they all recovered v. well, all laying. A week after we started eating eggs the sneezing started again, only watery discharge at the moment. Will another 10 day course of Baytril get rid of it or will it come back again. Could it be that the mycoplasma has left them with sesitive sinuses? I have also bought a cockerel who was and is fit and well. Will any chicks we might have hatch with it or will they only get it if in contact with the flock? Help? Sorry for so many questions.