I Have Been Doing A Little Bit Of Research Trying

I have been doing a little bit of research trying to figure out if I have a cavity in between my two front teeth or not. And if so what I would need to get done if I went to the dentist. But it is an almost non existent black like shadow that has been forming in between my two front teeth for a couple of months now. When I brush my teeth and floss it's not really noticeable at all but say if I drink soda or something and don't brush my teeth afterwards, it will start showing not long after. What makes me think it may be a cavity is the fact that my top teeth feel as if they are shifted and like I have a gap in my mouth. There is no pain but I can definitely feel something where my two teeth are. And the front tooth that mainly has this cavity is a little over top of my other front tooth. It's not that bad but I feel like if I don't get it looked at soon that it could be?