Hi. So About Three Weeks Ago, I Stepped On Something

Hi. So about three weeks ago, I stepped on something sharp. I have no idea what it was, I just know it wasn't glass. I immediately checked for an open would or blood, but I couldn't find anything. Fast forward three weeks later and foot feels really sore, but only when I touch it. There's no swelling or change of color. I'm just wondering, why it has yet to heal? It's not painful and I don't really feel it, unless I touch it.