Probiotics are an area where not a lot is known but much is being offered and claimed.
The theory behind probiotics is based on a relatively new concept known as the microbiome. We all harbor thousands of different species of bacteria in and on our bodies (see the Human Biome Project here). Our gut is essentially a self contained and very complex ecosystem. Derangements of this ecosystem have been implicated in all manner of illness from diarrhea, to Irritable Bowel Syndrome, diabetes, obesity, and even Alzheimers. Right now this is a lot of speculation without a lot of good evidence. Some of these relationships will no doubt turn out to be accurate and others will not.
Because it is well established that some gastrointestinal issues are associated with an altered microbiome this are has gotten the most attention. Studies have shown some benefit when treating certain conditions like antibiotic induced diarrhea. Others have experimenting with using these products to treat everything from irritable bowel syndrome to gas but as you have already noticed, the symptoms associated with these conditions are so subjective and can vary from day to day making it difficult to know whether these treatments actually help or are we just dealing with a placebo effect. Without a definitive diagnosis of your condition and well controlled studies to address whether probiotics help with that condition it is difficult for anyone to know whether these products will actually help or not. Its also possible that they may be harmful. Although there have been no reports of short term problems there is the possibility that the use of probiotics may have unintended long term consequences.
Unfortunately we are at the very beginning of trying to understand a very complex concept. With thousands of species interacting within the immense complexity of our own bodies the number and variety of possible interactions that could be going on is mind boggling. Some have tried to condense the whole field to an idea of “good bacteria” and “bad bacteria but this concept is simplistic and naive. It would be similar to studying the ecosystem of North America and dividing the thousands of species of animals and plants into good species and bad species but this approach is flawed. Mountain lions may be a bad species if you are a deer, but take them away and the deer destroy the vegetation and become the bad species. The truth is that we need the proper balance of organisms to create a healthy ecosystem and the optimal balance may differ from one person to the next. Products that claim to provide us with a dose of “good bacteria” may be helpful or may not help at all or may in some cases upset the balance entirely.
I would certainly discuss probiotics with your physician before using them for any condition you suffer from.
Antibiotics and Probiotics- Why you shouldn’t take either without a good reason