Taking large amounts of probiotics can really make the difference when having to take antibiotics. I have taken as much as 30 billion live active cultures at a time, with minimum detriment to my bowels. However, I tapered myself into that dose, and didn't just start out with that much.
Most places sell just "acidopholus" pills. They generally have between 1 and 5 million live active cultures. I would start out with probably 3 a day (breakfast, lunch, dinner) and watch that you don't take so much that you get diarrhea. Udo's choice (available at "natural food stores") as well as many other brands sell a probiotic blend. These often include 3-5 strains of healthy bacteria.
Also, real yogurt (without hfcs) can provide these active cultures too. I just found it easier to consume the pills over the necessary amount of yogurt.
Probiotics are actually something you can take all the time, and help you stay healthy, regardless of antibiotic use..