Door Latch

1997 Ford Contour LE - 2.5 liter engine - 128,000 miles - Driver side door won't close unless I'm outside and can push it really hard with my foot. The locks work fine. If I close the door with the lock off, the door will swing open and will not catch at all, but if I lock it first it will catch but not all the way. At least that way the door doesn't swing open when I'm driving. It acts as if there's something caught in the door (like when the seat belt gets in the way) but I've checked and can't see anything that would block it. I can close it all the way if I'm standing outside and use my foot to close it, but then have to climb over the console to get to the driver's side. This just started last night and it's not cold enough to blame it on the weather. Help!