Definitely speak to your GP and explain that it is having an effect on your career. You can talk to a speech therapist that may be able to help.

A lot of people are put off by "therapy" but it is worth going to an initial meeting with the therapist and finding out what the plan would be. If you decide that ongoing meetings is not for you then they may be able to give you a few exercises to do at home.

edit: http://www.stammering.org/adults_info.html

Here is some information. You do not necessarily need to speak first to a GP