I'd say "Welcome to the Club" but this is one club that none of us want to see any new members join. Yes, obviously with the pain that you've been having and the blood in your urine, you are a new club member and have a kidney stone(s). Since you're using a strainer, and by telling us that, I'll assume that you're using it all the time, IF you had passed the stone(s), you would have seen it in the strainer. It could very well be that the kidney stone has passed through your kidney and into your bladder, but not yet passed through your bladder to come out. The pain you felt was the stone passing through your kidney. You experience that pain and the blood as it goes through your kidney and and the jagged edges of the kidney stone tear at the very sensitive nerves etc in your kidney. You can also have some pain, but usually not nearly as much, when the stone passes through your bladder to your penis to pass on out. As to how big a stone or stones you have, you won't know that until it passes and you find it in the strainer or you get a cat scan to see how many you have, where they are located and what size they are. An ultrasound after it has passed will not show you any of that to my knowledge because the stone is gone at that point and there is nothing to measure or see where it is.
As to your pain coming back, it depends on the size and location of the stone at the present time. Again, if you only had ONE stone and it has already passed through your kidney into your bladder, you could still have some pain as it passes out, but it should be very minor compared to before. EXCEPTION would be if it's a very large stone and is blocking urine flow from the kidney, in which case its not in your bladder yet and you'd know that from discomfort you'll be having from urine backup into your kidney. Yours sounds to me, after 30 plus years experience and 40 plus stones, as though it's in your bladder and just hasn't passed out yet. As a male too, I can tell you that you probably will feel a very mild burning sensation as it does pass out your penis, but it will be very mild and won't last but a second as it passes out. . .