Flatulence with Smell and Bloating (long term-very embarrassing)

I have had a problem with gas almost my whole life (i am 17 now and it started about 5th grade). It was worse when I was younger and became better when I became a vegan two years ago. I always have gas, all day everyday, but it is worse and smellier certain weeks in the month. When ever I eat, no matter what it is or how small of an amount it is, right after I experience a bloated feeling in my lower abdomon, digestive sounds, and the appearance of a bloated stoamch and less than 30 minutes later I pass extremely foul smelling gas. It is horrifying and embarrassing and I have tried acidophilus and digestive enzymes but nothing seems to work. I feel fine if I don’t eat for a long period of time, odvoiusly that is because there is no waste in my intestines. Also, I have a bowl movement once or twice a day, but usually feel constipated during weeks when gas is the worst. any help would be much appreciated.