Hi Mikeladup,
Hello and welcome to the forum.
I am a bit confused by your question, since antibiotics do not help with anything that is caused by a virus, and the 'flu is a virus. If you took medication for a 'flu virus they were not antibiotics.....or at least I hope they were not, because if they were it would have been the wrong medication and the doctor was incompetent. Antibiotics are only effective with a bacterial infection, not with a virus.
Having said that, it is true that medications of various kinds can be triggers for flares in some people. If you were given an anti-viral medication it could have caused side effects for you. The side effects from antibiotics are hard on some people who have fibro or other similar conditions, and of course all medications can have side effects, some of which will cause reactions similar to a fibro flare, or can cause a flare in someone with fibro.
The best thing to do is make note, written down in a little journal or something you can keep handy, of the things that happen when you take various medications. Remember that correlation is not causation - meaning what you experience may or may not be a result of the medication. This is why you need to write it down, because if you have the same thing happen again you will have that information. A lot of managing fibro is a matter of personal experimentation for each of us because we all experience it differently.