Firstly Oregano oil is not considered an 'essential' oil. Essential oils are from plants/flowers and they carry the 'essence' of the plant - or as some vitamin bottles say - 'energy imprint', which I guess means the frequency. Essential oils are used mainly in perfume creation - because of their purity and superior properties, then when we found out they were beneficial for our health we started to use them in aromatherapy, though there are now some unscrupulous types offering fakes and whatnot.
I was given oregano oil once by my doctor and didn't see any difference in my condition at that time so threw it away. If I was you I would keep searching, try a book by kathi keville on herbs etc.