Is my cat ill or just aging?

Hi, just wondering if anyone had an experience or insight into whatever is happening to my cat.Shes approximately 11 years old and has always been in good health until about a year ago. The first sign of a problem was what seemed to be an abcess on her cheek, where the hair all fell out on the cheek and the skin below was red, angry looked pretty sore. So we took her to the vets and they gave her antibiotics, it improved slightly but has never gone away completely and every now and then she has a flare up and we take her back to the vet, who usually gives her antibiotics. On one occasion though, about 6 months ago when we took her to the vets they said they would not give antibiotics again but that this time the options were either to put her down or to pay for dental treatment which was £250, so we took out a loan (which we are still paying off btw) and paid for the dental treatment. This was deemed necessary because of her new symptom of contant drooling. Anyway, they said that if the treatment didn't solve the problem, they would then do a diagnostic test to try to discover the cause, I wanted them to do that there and then but they wouldn't, they insisted the dental treatment was the way forward. Anyway a few months ago, it flared up again, so my OH took her back to vets and somewhat disappointingly they sent him away with another big bill and antibiotics??? What happened to the diagnostic test? I should mention that during this time she has also had a bald patch about the size of a coin on her back, which goes through phases of being bright red and angry looking, to a scabby brown appearence. On showing the vet this about a year ago, she felt it wasn't connected. However I'm not convinced because it seems to be behaving in much the same way as the sore on her cheek, going through phases of looking really sore, then appearing to heal slightly, then flaring up again. Like I say this has been going on a year or so and we have spent hundreds of pounds at the vets during this time and nothing has improved and the constant drooling all around the house, is driving me mad, I am heavily pregnant and due to have baby within a matter of weeks and I'm concerned about the hygiene issues. To make matters worse yesterday I noticed a new inflamed looking sore on the cat, this time under her chin. Aside from all this however, she still seems in good health, appetite is normal, activity levels normal, but it looks like its getting worse and I feel like the vets aren't taking it seriously. Anyone have any ideas what is happening to her? Anyone had a cat with similar symptoms?

thanks everyone for your quick responses, I think you're right, i think we do need to get a second opinion from another vet, I don't know why I didn't think of that before! I let you know how we get on