How to get better at Vowels?

How to get better at Vowels? Hi, Its my first time posting here. Unfortunately, I'm also a stutter but its very mild. It started at the age of 14 (I'm 22 now), before that I won many speech competitions in my school but now I can't do public speeches. I can easily manage day to day activities which involves speaking but It gets worse when I'm stressed or anxious. I struggle a lot on words which start from vowels (A,E,I,O,U). Is there any technique which makes it easy to say these words? Thanks in advance and I hope that each and everyone of us will get over this problem.