Why so much phlegm in my throat?

When I talk a lot, I have to clear my throat because I start to rasp. And I have to swallow the phlegm again so it doesn't clog up my throat again. My mother says I was born with the problem of blowing my nose often, (along with my sister who also has a lot of phlegm in her throat but has to blow her nose much more commonly.) Explanation, anyone? I would also like to know how to get rid of this pesky problem.