What's the secret to be able to get real big with air?

Usually I can get to a decent feeling of fullness with air inflation (anal). But whenever I try to push for a little more, I feel sick and unwell. Idk if it's because too much air is in the stomach or if I'm not burping enough. But something keeps me from getting real big and round for a bit...

If you guys have any suggestions, I'd be pleased to hear your secrets! 😊