I Constantly Smell "mustiness" ...no Matter Where I Am But

I constantly smell "mustiness" ...no matter where I am but especially in my home. I have no known allergies. I cough occasionally and it is productive...somewhat thick and opaque. I sneeze occasionally. Sometimes wake with a very slight headache. Our home is air conditioned but we clean and change our filters often. I clean our drains and the trap in my dishwasher. We empty the trash frequently from our kitchen...more than 1x daily. Any thoughts?