My teeth are stained?

So I dip occasionally and sometimes smoke but I have been doing it for a while. I haven't really done either in a while and I am not a heavy user. I do however drink a lot of coffee and out of nowhere yesterday I got stains on the inside of my lower front teeth. The tooth is not stained just the inside. I did not brush my teeth yesterday (I left my toothbrush at home and was staying over a friends house, I take EXCELLENT care of my teeth, floss, brush, and use mouthwash twice a day) and now I have these horrible stains on the inside of my teeth. I tried using baking soda, but I think I took off part of my gums and it didnt really get the Stain off. Is this temporary, or should I get this checked out? I had no prior stains before yesterday. Also, how can I tell if my gums are receding?