There are all kinds of side effects to taking antibiotics, and they should only be taken if absolutely necessary. For one thing, there's the development of antibiotic resistant bacteria. For another, they kill off beneficial bacteria as well as toxic ones, and some of these beneficial bacteria play a role in mental health,such as producing B vitamins. The connection of probiotics to mental health is one of the hottest research topics in the medical field. But anyone can have any reaction to a particular prescription drug; the body isn't adapted to any of them. But be wary of quitting an antibiotic once you start taking it -- it can also produce antiobiotic resistance in your body. Once you start you usually need to finish the dose. In your case you quit pretty close to starting, but again, be careful doing this.