Loud Burping and Vomiting

My 3 year old son drinks sodas and eats cookies on occasions. He burps extremely loud before and after he eats. It doesn't seem to happen before or after certain foods or a specific time of day. He also vomits at least once a day. He will be sitting there doing nothing and then he will just vomit. This also does not occur at certain times of the day or after he eats certain foods. He will be playing or laughing sometimes maybe even talking and then all of a sudden he is running for the trash can or toilet to vomit. I am worried that it may be something to do with his digestive tract but am unsure and would hate to take him to the doc for test after test for no reason. If I could just get an idea for now it would be great, that way I can at least start somewhere. I read somewhere in these forums that it may be linked to gallbladder problems.