When I first started
vaping back in '012, with Blu and then pens like eGo & Kanger, I coughed quite a lot. Many other first-starting vapers did as well. When you go off analog cigarettes, your body, lungs, cilia hairs, inner cheek lining, etc all begin to heal and coughing is helping your lungs dispel tar and other nastiness from those anaolg cigarettes. I would wager that you're gonna hack quite a bit, for a good while. You can try different ratios of VG/PG and the other things the previous commenters suggested to help ease you into the transition, just bear in mind that coughing out the analog cigarettes' nasty accumulation is a good thing. The coughing will eventually pass as your lungs heal and cilia hairs regrow.
You may find your mouth will get very dry and you could possibly develop some very painful sores on your tongue and inner cheeks, and this too (should it occur), will also pass. Drink lots of water and keep on keeping on.
It's easier for some than others. My transition was brutal and I fell off the wagon a few times, but in the end, when you're cigarette free, it's worth it.