Try not to worry too much about something you can't predict! You could just as easily be one of the many people who have no lasting problems from it. I'm glad you're off it now and taking a probiotic. Hopefully it's a good quality one and in a high enough dose?
Really anyone on antibiotics should take probiotics. I don't know how many times I've had a friend taking antibiotics and complaining about major digestive system issues and I tell them to take a probiotic supplement and they don't believe me or whatever and procrastinate on it, and when they finally take it as suggested they are like "Wow, my stomach feels way better" - why don't doctors inform people of these things!? 8)
Only other things I can really think of to do are to be really kind to your health for a while, like eat healthy, avoid drugs/alcohol (especially alcohol right now, since both tetracycline and alcohol are hard on the liver), make sure you get lots of sleep and exercise, and try to keep your stress at a minimum.