Belching that tastes and smells like sulphur (rotton eggs) usually followed by a painful stomach ache. this lasts till i puke up. what can this be?

Giardiasis: The "purple burps" are famous. There are other possibilities.

I am not sure: At all mainly since you are so young. Your complaint is usually the case of motility namely gastric emptying problems. Other option is infestation with a single cell parasite giardia lamblia but this goes with diarrhea you do not mention. I suggest see a GI specialist to check your stomach emptying. If that would be confirmed, blood test r/o an auto immune condition is in place.