I'm sorry to hear about your cats lip problem and that it doesn't seem to be clearing up.

I personally haven't experienced anything like this with my cats so can't really offer any advice with that, sorry.

But, if you really do feel as if your vet isn't as good as you want them to be then I'd suggest going to another vet... even if it's just for a second opinion.

I have had a problem with a pet before and didn't like one vets answer, so I went elsewhere for a second opinion and got told something completely different.
Sometimes it pays to shop around, even with vets.

Good luck and I hope you get the problem sorted asap.