Firt things first, needless to say that I'm still a newbie haha.
I've been learning how to model with extruding vertex and faces, instead of starting from a cube.
Everything went pretty well until I decided to add a Subdivision Surface modifier to smooth everything and I found this(Also happens when I right click and check shade smooth):
Also I let you see the X-Ray version, which made worry:
So thanks in advance and any help would be appreciated :3