Sounds to me like you may have some delayed gastric emptying. May be the result of a passing virus, it may be slowed down by some medication like opioids, clonidine, calcium channel blockers and others, recent alcohol, or other relatively benign cause. Often it just happens. Diabetics often get this too, fancily called gastropareisis, and some get put on meds for it if it’s too severe. It can also be a sign of various neurologic diseases, but I’d not worry about that until/unless it becomes recurrent.
I don’t think it’s likely to be related to the peanut butter being ‘stuck’ anywhere. While not impossible, the fact that you’re doing so much burping makes me think of delayed gastric emptying.
However, I’ve not had the chance to ask you a dozen or more clarifying questions, nor examine you, so I only posit this tentative diagnosis with about 50% confidence.