Welcome to the forum mygirl! I am sorry to hear about your parrot and there are so many vets out there that do more bad than good. One of our members lost her bird due to wrong vets, wrong medication and wrong or no tests.
Please try and locate a different AVIAN vet because the one that you are currently using should have given you probiotics like Oom Bobby said.
Please keep us updated.
As You've stated antibiotics can destroy both good as well as bad bacteria, not sure if you had an avian vet put your fid (fid=feathered kid) on antibiotics or possibly yourself, but you'll have to put him on probiotics in order to help regain the good bacteria which is essential for proper digestion, if you don't have an avian vet I would suggest you seek one if there are any in your area, as I'm not a vet myself I can't say the regurgatation is a result of the meds, but there is that chance that it is, better to be safe than sorry, good luck