I have trouble in uttering certain words. How do I overcome this?

Hello doctor,

I have a difficulty in pronouncing words that start with a vowel, for example, 'experience' or 'academic'. Whether the word is in the starting or the middle of the sentence, there is always a difficulty. It has been around two and a half years since the problem began. I have to take a momentary pause and thrust it out forcefully. There is an unusual feeling in my chest too when I force myself to speak such words. The special aspect of this problem is that there is no problem when I practice saying these words in my room. But, when I speak to others, it gets revived. I need you to suggest some speech drills, breathing exercise, or special precautions, so as to help me get over this probelm.