I know cottage cheese expires... but how to tell?

I know cottage cheese goes bad. And I know with certain foods it says it will expire by a certain time but that’s without taking the whole opening it and using it into effect. I’ve had this cottage cheese for a while, and well, I’ve always thought it smells bad… it always has a bit of a bitter/sour taste and it looks gross. I can’t tell by those factors if it’s expired. Any ideas as to cottage cheese’s shelf life?