There's a couple of things that can cause low vapor on exhale. One is insufficient voltage for the resistance of the atomizer and the other is
juice. PG will produce noticeably lower vapor than VG for the same voltage/resistance ration in the atomizer. On a standard eGo battery, the output voltage is about 3.4v. That matches well with a 2-2.5 ohm coil. a 2 ohm coil should give you clouds of vapor with a good
juice.
If you inhale and hold vapor, the amount of vapor is reduced on exhale. Nic is absorbed from vapor more efficiently in the mouth and sinuses. The lungs coat with PG or VG, but the larger particle size of vapor as opposed to the ash size from smoking tobacco prevents nic from being absorbed in the lungs at the same rate as burning tobacco.
If you want good exhale vapor, inhale shallowly and exhale through the nose. The sinuses are more efficient at absorbing nic from vapor than the lungs. You can even absorb nic from vapor by just holding it in your mouth for a while before blowing it out.
A mechanical cause of low vapor is a flooded atomizer, carto, or tank. That's usually exhibited by gurgling on inhale.