I am definitely not a doctor but it sounds gastrointestinal, have you been eating something different lately? I eat onions all the time, soups, perogies, sauces, raw on sausage on the bun with no problems, this one time I bought a bag of onions that gave me huge problems, I really thought I was having a heart attack(there's a history of it in my family so I was worried about it since I was a heavy smoker at the time), went to the ER, sitting in the waiting room burped like really really loud and like half the pain went away, laughed it was so loud and the ppl in the waiting room which was packed were all staring at me, checked out and left the ER, didn't realize what it was till the next time I ate those onion's..
Avoid these Gas Causing Foods to see if it helps and chew your other food better if you don't..
- Baked beans
- Vegetables: Brussels sprouts, Cabbage, Cauliflower, broccoli, onion
- Chewing gum
- Whole grain: whole wheat
- Fruits: apples, peaches, pears
- Sorbitol: Sugar free candies, gums
- Carbonated drinks
Oh and if you're worried go get a second opinion!
Edit****
Also if your taking deep lung hits it may add to the problem because of extra pressure.