It feels like I have liquid in my ear when I yawn or hold my nose and blow. What is that.?

Pressure change. The middle ear is a closed space, except for a "pop-off valve" called the eustachian tube. The maneuvers you describe can force the eustachian tube open leading to some small pressure changes in the middle ear. This may be the sound you are hearing. You might also have some actual fluid in the middle ear. A quick ear exam can help differentiate.
Eustachian tube. Patients with similar complaints often have a problem with their eustachian tube (the tube that connect the nose to ear). Although they think they have liquid it is usually related to the fact that the tube hasnt opened properly - usually related to some nasal congestion or allergies). These patients also have problems clearing their ears during flights.