Sometimes when you have a cold or head infection, sinus infection; this causes swelling and irritation of the eustachian tube which is a tube that runs from the back of your throat up into your middle ear, on the inside of your eardrum. The purpose of eustachian tube is to equalize the air pressure behind the eardrum and it's done so mostly by swallowing; which makes the eustachian tube open up and close and allows the air pressure to equalize. When you have a cold this actually can't happen and you get pressure and pain behind your ear and it gives your eardrum less mobility because it becomes thick in one position due to the increase pressure behind your eardrum and or less pressure where the air has been absorbed by the inner ear and allows the eardrum to retract. In either case the eardrum has less flexibility in the home, reason you're here is because the eardrum is free to vibrate back and forth and respond to sound waves coming to it from the air. When it's fixed, each pressure being too much or too little behind the eardrum it gives you a sense of the ear being full or stuffed up and a lot of times you can sense this also when you fly the airplanes or change altitude. The simplest way to try to clear is to hold your nose and blow gently until you hear that ear pop or what you're doing is actually opening up your eustachian tube by pushing air from your mouth up through it into the middle ear and that equalizes the pressure temporarily to allow the ear drum to have more freedom of movement; therefore you clear what feels to be stuffed up here.