Hi Nana -
Welcome to PSG!
Don't worry -- sometimes it takes a while to get to the bottom of a problem, but we've got plenty of very knowledgeable folks here (certainly including MrTom) and 99.9% of the time, we'll figure out the source of the problem and get you on your way. However, be advised that almost always we have ask quite a few questions to get all the info we need to accurately diagnose a problem.
With respect to terminology, using the exact term does help tremendously because often there are similar sounding terms with different meanings, but don't fret about it too much -- you'll pick up the terminology as you become more experienced. BTW, FYI, another term that is almost a synonym for "document" is "canvas" (...at least, in Photoshop). Of course, just to make life difficult, Adobe decided to call essentially the analogous concept in Adobe Illustrator, "Art Board", LOL.
With respect to the probable source of your problem, MrT (that's the short version of his screen name that I use because his real name isn't actually "Tom") is almost certainly on the right track. That being said, let me mention that some time ago, I helped someone with a similar problem. What made me think of it was your statement, "I never had this problem before". In their case, thinking that they were helping matters, someone changed the resolution setting on their scanner so that after the change, it was putting out vast larger (in pixel dimensions) files than it had been. So, when she cut and pasted files produced after the settings were changed, the result was exactly what you are seeing. Your problem could be caused by many other things, and this is somewhat of a long shot, but do check that no one has mucked around with your scanner when you weren't looking.
Best regards,
Tom M