How can I not stutter as much?

So I'm 18 and I've always had speech difficulties my whole life. I've been to a couple of speech therapists but that did not help. I have asked family and best friends on how I can get better with my speech and they all said to me "slow down and think about what your saying before you speak" so I tried that out and it helped me a little bit but not much. I recently took a public speaking class to hopefully get me better at public speaking but it really didn't. I mean I can talk almost like a regular person but it's that I have a hard time saying certain words sometimes. In other words, I have a hard time spitting out certain words. I'm not sure if I'm stuttering because I get nervous or if it is because of something else.

Can you people on Yahoo Answers help me out please? Thank you :)