My advise is this and its based on my own experience and should save you lots of time, money and worry in the long run.
Find a doc that will do a stool test for you. Talk to Breakspear Hospital in England if you are from Ireland or England. In the states I am sure you can track one down.
This will give you a definite answer. Then when you know for sure what is causing the problem (bacteria/ parasites etc) you can take a definite prescription and or herbs that will hopefully start to sort things out for you.
I spent years guessing what was wrong and in the end it turns out its a parasite which I am waiting to get treated.