@Kira285
Kira, I assume from your post you are renting a shared listing where, not only are there common areas but your sleeping arrangement is in a common area, ie: you are sleeping on a sofa bed in a living area!
Was your expectation that you would have a private space when you booked this listing? It is common in backpacker accommodation to have a lack of personal privacy, but you accept that when you choose to stay.
If you booked a private space and your host is entering that private space, that is not allowable and Airbnb does not condone that.
Speak to the host and say in a non confrontational way you do not feel comfortable with he/she entering your area and can they please refrain from doing so when you have an expectation of privacy.
If the host refuses you can apply to Airbnb to have the stay cancelled.
But I am afraid Kira it all revolves around the description of the listing you accepted when you booked as opposed to what you are experiencing!
Sorry I can't be any more help than that!
Cheers........Rob