So your able to pull liquid through the wick holes and into your mouth, and your able to push vapor out of the vent holes at the bottom of the tank, but you are UNABLE to get vapor from the wicks to your mouth. Sounds like you got yourself a blockage. There is an air blockage somewhere. Does your tank fill up with vapor at all? If it does, then the connection from the head/coils to the mouth piece is broken. If that connection isn't broken then it most likely is a blockage of air somewhere. It can either be at the wicks or at the 510 male venting holes in the portion that screws into the female 510 connection. You may want to give pulling your protank's post a try. Use a flathead and pull the post in the center of the male 510 connection down a bit until it is flush with the bottom of the 510 connection cylinder. Once you do that, you should be able to screw the protank in enough and back it off enough so that the air holes are indeed exposed to enough air to allow for a draw.
If pulling your protank's post does not work OR if you don't even want to try pulling it, you want to be looking at the wicks & the PG to VG ratio of your juice. Since your getting juice into your mouth, your wicking doesn't sound like its bad. But, you may have wicked so much that now its creating a vacuum effect every time you take a draw. If your using a high VG juice and your wicks are extra thick for some reason, (mistake at the factory) then you'll need to thin out the wicks and/or add some PG or distilled water to your juice. I don't THINK this is your problem, but it may be. I'd take a look at the wicks, see if you can see bubbles coming out of the wick holes when your take a draw. If theres no bubbles, or its very hard to produce a single bubble, your wick might be stuffed into the wick holes too tightly.