Suddenly decrease exposure and likes

I have a business account and have been wiroking it up to a solid 800:likes 4000:exposures. But 4 weeks ago it suddently decrease in one day and are still struggling. Im down to 350:likes 2000:exposures avarage.

Have someone a clue of what this can be? How can this happen?

Which niche you are working on and how is your reach and number of campaigns ?