Here's the bad news. The big difficulty with any attempt to reach 100% certainty right now is that it can turn up in your dreams. So if you think you're feeling that you are awake is a guarantee, or even evidence, that you are not dreaming, I'm afraid you are on the wrong track.
There is a real possibility that you will wake up one morning and realize that while you were asleep, you dreamt that you were awake. In fact, if you dream you are having any experience, you are already dreaming that you are awake. You may not have noticed that, but only because your dream did not lead you to ask the question. But it could - or at least you cannot guarantee that it couldn't.
(The puzzling possibility is that one might dream that one is dreaming - would that be a dream within a dream? H'm. I've never heard of that, so I shall worry about it when it happens.)
Is that just a logical possibility? It certainly is that. But I was once told by a friend that he had learnt to tell whether he was dreaming or not. Sadly, he never told me what it was. Why? Next time I saw him, he told me he had dreamt it.
Here's the good news. You can tell for sure when you have been dreaming. You were taught how to do that at a very young age when you woke up distressed in the middle of the night and woke up everyone else. They taught you that you had dreamt about leaping over tall buildings to escape from the wolves. For once, the adults in your life were right.
I suggest that the problem with the question "Are you sure you are dreaming right now" is the "right now". The answer is, No. But you can tell in retrospect.
If personal experience may be allowed to intrude, there are one or two incidents in my life that I thought were real for years. Eventually I worked out that they could not possibly have been real. Time will tell.
Incidentally, a dream within a dream would only count if the dreamer dreamt about waking up and realizing that the previous dream was a dream and then wakes up and realizes that the whole thing was a dream.