Hard clear bubble on my gum on my lower jaw. What is it?

I have a clear protruding bubble the size of a pin head.. maybe a bit larger that started out with a little blueish dot on the gum covered by a clear hard bubble. Located on the outside below my second to the middle tooth on the bottom gum area. After about 6 mo. it has protruded out more but not grown in circumference. Its very hard and has gotten cloudy. Its sort of located an 1/8 of an inch down from the tooth and in between the next one, not really on the spot where the root would be located. A dentist, not my own, saw it in Jan. 2011 and said just to keep a watch on it but didn't think it was anything. The hygienist had noticed it and called him in. Now it has protruded almost twice what it was. What could this be and should I get to a doctor, if so, what kind? Dentist, regular doctor? Where do I start? Its not sore and the gum seems healthy there.