Speech pathology graduate student here. Came here to agree with natabean. Your brain uses a different, more manual neuro-motor pathway when speaking English because it is your second language and less automatic. You'll probably find the same thing when speaking Arabic and changing your accent. However, this is not a long-term fix since your brain has a way of changing neuropathways to make them more automatic. To answer your second question, you will find that starting a sentence with vowels is easier than consonants such as 'sh' because your vocal folds in your throat need to vibrate to create the vowel (this is called voicing). Once the vibration starts, it's much easier to keep it going. Since I am in the field of speech pathology and have seen the difference speech therapy can make, I recommend seeking a professional to help you. They can teach you more about stuttering, techniques to help you minimize your stuttering dysfluencies, as well as some counselling in regards to any fears of certain words or social situations. There is no cure, but the therapy is evidence-based and really helps. Feel free to ask me more questions and I'd be more than happy to answer them!