Its normal. We all have letters/vowels that are specific to each of us but the underlying issue is the same. The situations you mention just highlight that confidence in yourself to speak will definitely help. I know its easy to say but you must find a way to build it through any victory, as small as they may seem. You will have setbacks but overtime you will improve. If you are calm and confident, it will be easier. Take note of those small victories (order at the restaurant that you nailed, rebuttal that went well, etc..). I suggest consulting a speech therapist if possible. It helps to structure your approach to speaking and gives you concrete strategies. There is no quick and easy solution as overcoming stuttering requires a holistic approach (body and mind) but to start, you can try focusing on breathing and making sure your esophagus is always clear and open when speaking. Second, instead of focusing on the first syllable, you can break it down and focus on the second. For me, the long words starting with D as in "Development" are hard so instead of focusing on the De, I read it in my head as de-VE-lopment and it works like a charm. Hope this helps.