The good bacteria keeps things like yeast in our gut at a manageable level. When you take
antibiotics it kills all the bacteria, good
and bad,
and therefore things like yeast grow and cause major problems.
First thing to do is to stop taking antiboitics, start taking probiotics (at least 10 billion cultures), start a low fodmap diet (google it), and hopefully these things will have you feeling better in a short amount of time.