Oh, ok, that's not ideal antibiotic. If ear infection doesn't improve, then that's why. And, if your past allergic reaction is not known or not full out anaphylaxis from penicillin, you can try one of the many cephalosporins, like cephalexin
Gut flora will always be affected by antibiotic use and probiotics have limited use in restoring this. Many are poorly formulated and barely survive GI transit. The suggestion of fermented foods is good if you have a taste for them as they contain huge numbers of organisms ensuring a better bioload that can reach the small intestine.
I am a skeptic at the moment regarding gut microflora. I think we are too early in the research to have a good grasp of what is "healthy" or "optimal". It's likely we will go through many revisions of thought regarding this topic just like every other scientific topic studied.
I just had to go on an antibiotic run for a gross stye i had about 3 weeks ago.
I was VERY proactive about it and after it got bad, walked into an Urgent Care clinic where they put me on 2 different anti's and said if it doesn't get noticeably better in 24hrs, go to the ER.
I knew my gut was fucked from this but they told me to go and buy a couple packs of FloraStore. I had no idea that you cant take antis and pros at the same time, the anti's will just kill everything so you need to really space them out. But i guess Florstor works differently. Either way, went thru 2 packs of florastor no problem and also kept kefir, greek yogurt and sauerkraut in.