Ok so you are very confused. That visa that is in your passport, you needed to enter the US with that visa. There should be stamp on that visa for the date you entered the first time with that visa.
Since you have been coming to the US every month someone at the border must have noticed your Visa. Did they ever ask you about it?
Once you entered the US with that visa the very first time. It became your new home. You left for no reason.
So please tell us everything you did that very first time you entered on that visa. Did you tell them you were moving to the US or tell them you have a visa? Did they take you to secondary (inside) to stamp it?