When you say someone do you mean a specific special someone or do you mean someone as in anyone? I would say its normal to perhaps blush when you're talking to someone you have a crush on but to blush when you talk to anyone is not normal.
Severe social anxiety my friend. If I were you I would seek professional help via a three pronged approach of speech therapy, psychotherapy and low dose antidepressants and anti-anxiety medication. Just my non professional opinion of course.