It can take a week or two to get used to the dry vapor. It's quite different from the smoother smoke of a cigarette since tobacco has chemical additives. Plenty of water helps and so will gum or throat lozenges.
If you are direct inhaling, it can irritate your throat. Also try drawing in the vapor with some outside air, holding it in your mouth first and then gently inhaling for a while until you get used to it. Some people say that using your tongue above the mouthtip to block direct flow of the vapor to the throat can help. Hot dry hits when you are new can irritate your throat also, it takes some getting used to keeping an atomizer wet, especially a small one such as the 901. Drip on the atomizer bridge a few drops each time you refill to help keep it very wet.
If it continues, try switching to a VG liquid (or buy some VG from Walmart and cut your liquid to see if it helps, and then just buy some new VG liquid). PG reactions can cause many things, including excessive post nasal drip (some saline spray can help) and that could have you coughing at night. A visit to an ENT physician could determine if that is the cause of your coughing.
Last... it could also be a reaction to the flavor you're vaping (have you tried a clean atty and a different flavor?). Some have an allergy reaction to flavorings, and symptoms can be mild like a cough or more severe like tongue swelling or mouth sores, so it's good to be aware if it only happens with certain flavors. Try to buy small sample bottles from vendors so you can find some you like and may be milder for you.
I didn't have the instant loss of desire for a "real" cigarette, but vaping really has made it possible for me to get over it. Best of luck to you.
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