From what I have read, it's very hard to get rid of bacterial overgrowth and you do need to take antiobitics for a while. No, it's not a lifetime thing, but I have seen, for certain types of bad bacteria, recommendations of up to 6 months (that's pretty extreme, if you think about it!). But that's for like antibiotic-resistant c. difficile, so you shouldn't need anything that extreme.
Are you also taking probiotics? By taking them during and after the antibiotic treatment, you can help get your gut repopulated with good bacteria. Your colon is a lot like a street with houses on it: bacteria live in the houses. Now, like any neighborhood, there are only some many lots where you can build houses. Once the neighboorhood is full up, bacteria have to pass on down the road (and out of your system). Antibiotics evicts everybody from their houses en mass. If you can introduce probiotics to your system while you have a lot of houses sitting vacant, you can rebuild your intestinal neighbohood with mostly good neighbors. If you don't help reintroduce them, though, any bad bacteria that survived the antibiotics can very quickly multiply and take residence back up in all of those empty houses.
A number of doctors have found that people recover better when they do a 1-2 punch with the antibiotics and then the probiotics.