Why wont my NHS dentist listen to me?

I've had gingivitis on my bottom teeth for a few years now, over the past year it has turned into periodontitis, the gum has completely gone between most of my bottom teeth, there is a clear 3-4mm gap there and I'm scared that my teeth are going to fall out. I'm only 19. I'm quite shy and I've mentioned this to my dentist before but he just said "use a soft toothbrush". I brush and floss daily, it's still not going away, it's getting worse and it's starting to hurt, I'm despairing here, what can I do?