Obviously you should see a doctor and be properly diagnosed regarding both the itching and the possibility of a sleep disorder. But here are a few additional facts until you do.
You don’t mention HOW MUCH Nyquil you are taking. Are you aware that it’s 25% alcohol? This translates to 50 proof in liquor terms. This is a significantly higher alcohol content than wine or beer. I’ll leave you to do the math on how many cans of beer or glasses of wine your nightly amount comes to.
Nyquil also contains significant amounts of Tylenol (Aceteminophen) which is now widely proven for liver toxicity.
For both the itching and sleeping, you’d be far better off with one single ingredient which is used for allergic reactions and has a side effect of drowsiness.
The other advantage it has is a long long history of a wide margin of safety. It’s been available for ages and cheap as dirt generic and OTC.
I’m referring to Benadryl (Diphenhydramine). I’ve been taking it for well over ten years and no doctor has ever raised an eyebrow or cautioned me against it. I always include it when listing the medications I regularly take. I’m taking it primarily because of my allergy and sinus problems but the slight effect certainly doesn’t do any harm for me.
You mention being a natural night owl. That category includes you and me and approx. 30% of the rest of the population. So being a night owl is not a sleep disorder, per se. It just means that your body has atypical Circadian rhythms. It’s basically genetic since it involves involuntary physical body processes.
It can be overcome with strict behavioral modification aided by a specific type of light therapy but there are also other solutions.
But the primary problem comes from a natural night owl trying to fit into an early bird schedule. I used to think I had insomnia until I came to a time in my life when I had the freedom to make my own schedule. I sleep just fine. No insomnia at all. I just sleep a very different 8 hours than the other 70% of the population. That’s all. It’s not a sleep disorder.
If the reason you’re knocking yourself out with booze (that’s basically why the Nyquil works) every night is in order to keep to an early bird schedule, then that’s what you need to be working addressing with medical guidance.
Knocking yourself out with booze is NOT a long term solution. It will come back to bite you in the butt one way or another. The itchiness is the mildest of the problems you could eventually end up with.
Take the time and energy to get yourself properly diagnosed medically so you can get a long term solution that’s workable for you.
A regular MD is the first step but you should seriously consider seeing a sleep specialist (yes, they do exist) and perhaps having a study done at a sleep lab.
You need to deal with the root of the problem. You’d be amazed at how helpful seeing the right specialist can be.