Yes it sounds as if the Eustachian tube is blocked. It is often as a result of a cold or ear infection. It allows air to pass from the throat to the middle ear to balance the pressure. Some times yawning,swallowing or holding the nose and gently blowing will temporarily clear it. If it is a cold then it should clear after a few days, if an ear infection then antibiotics may be needed. Presumably your doctor saw no signs of infection so it's just a case of giving it time. Flying with blocked tubes can be painful and if you have problems such as decompression then you can easily damage the ear, so it's probably best to stay at FL00 for the time being.