Outside of a possible placebo I can only think of two reasons for this to occur and both of them are rare occurrences, but possible.
1. It's laced with a synthetic cannabinoid. Check the legitimacy of the people you are fucking with. Then double check it.
2. Full spectrum CBD oils usually have a minuscule amount of THC, almost always completely negligible (under .3 percent--the legal limit). Very rarely however, with concentrates such as full spectrum cbd oil and due to the current wording of the Farm bill, you might stumble across a batch with slightly larger amount of THC (maybe .6 percent) that was derived from legal hemp. Of course the amount of THC is still really small for most people but it's possible to feel it if you have no tolerance.