Lumps on my horses spine

I have a Fox Totter who is about 21 years old. I mostly do hunting and packing on him. Lately I have notice that his spine has three lumps on it. One is a little above the hip bone and the other two are father back closer to his tail. I was thinking it might be from the saddle not fitting, but the lumps are located behind where the saddle sits and it does not seem to bother him when I touch it. I am thinking of bringing a chiropractor out, but I have never used one before and do not want to spend the money if I do not even know if it will help. If anyone has any ideas on what the problem could be that would be a lot of help...Thanks!