I've had problems with sleeping since being a teenager, I found night nurse used to work quite well but obviously you can't be hoying back a measuring of that every night!
Remember that nicotine is a stimulant, it raises your heart rate and stimulates neurotransmitters in your noggin', this will have an affect on being able to put yourself into sleep mode so I generally try not to vape 20-30 minutes before bed.
If you really cant not vape before hitting the hay follow a few exercises to get your body and mind 'ready' to shut down for the night, it's how I've eventually overcome my sleeping problems.
At first I'll lay flat on my back in complete darkness and concentrate on letting all the tension run out from my body, focusing on my feet first and working my way up through my abdomen to my head and letting every muscle you can pick up on relax.
Secondly I'll start concentrating on my breathing while keeping my body relaxed, 10 big breaths in through the nose and out through the mouth and focusing completely on your lungs and your breathing. If you find yourself doing it automatically and thinking of something else (such as a daily worry or something else that's going to kick your brain back into gear) just simply bring yourself back to concentrating on your breathing, big breaths in and out. In practice it's very similar to beginner meditation.
Thirdly, once my breathing has settled and my body feels weightless, I'll start to let my mind wander, but importantly you control your thoughts at the end of the day so think of something that will make you happy. For example a place you would love to visit such as sitting on a huge mountain top overlooking some awesome scenery, anything that makes you feel at peace really. If that fails then another thing that works for me is mild problem solving, I'll think of how I can improve my vaping builds or if I designed my own custom mod, what the finished version would look like. (If you can't think of anything else a foolproof thought process is all the things you would buy if you were a millionaire)
But again, try not to think of anything that's going to make you too excited as that will disrupt the whole process and throw you back to square one.
I had a late night last night without my vape, so when I got home it was straight to bed for me and obviously I couldn't resist a vape, I did exactly what I mentioned ^up there^ and I think I drifted off after 10-15 minutes. It's all in the mind!