It sounds like your good bacteria have been wiped out, most probably by antibiotics and it was enough for the bad (probley candida) to take over.
The problem with most probiotics is they are stripped of the breeding and growing rights so you have to keep topping up therefor fueling the inventor and labs etc. After all you wouldn't want a drug to cure the common cold because you wouldn't be able to keep selling lemsip/beachems etc.
Proper good strong bacteria that actually teach your immune system how to recognize virus/foreign matter as pathogens and potential danger can be obtained from your mother. (Breast milk) Obviously you can't go out and drink your mums milk now lol but no one can disagree that even modern science cannot replicate breast milk. Some have come close but even a malnourished mother can still develop good breast milk.
So the best thing to do is to find a good probiotic such a CP-1 and not yakult etc.(Not sure on optibac) I am no means a doctor but you can decide for yourself if you read through this website http://www.yeastinfectionadvisor.com and you can run a test your self at home! most people don't even know they have an overgrowth of bad bacteria.
cp-1 is the strongest chain of bacteria and a combination that do not compete with each other. Also they are not filled with sweeteners and other useless crap. ALSO the most important thing, cp-1 guarantee's that there will be 50million by the exp date. Thats over half of the average. Remember that your stomach has billions upon billions of different bacteria all competing etc so 25million bifadus (sp) is a drop in the ocean.
Most doctors don't believe in candida and will push you out the door with some IBS tablets to suffer for rest of your life. These bad bacteria if not kept in check are a serious serious problem that lead to other problems like a leaky-gut. Do you have allergies now? or developing them? I have loads, can't eat nothing thanks to candida
Cancer can develop! Your liver can start to be overtaxed and tire of having to keep cleaning the toxins from your body that the bacteria leave. Your pancreas could be working over time to keep your blood sugar in check.
Anyways I don't post must I just lurk about but I know a little about this subject so thought Ill try and help.