You have utilities run under there and the ground had settled. Probably your water main. It will get worse. Caulk it up per the directions on the tube. Use a sealant specific to concrete and plan on doing it every year. Some stuff is self leveling, and some is not. The self leveling will need the bottom of the crack sealed first or it'll just run right thru your crack.
What do I do so this doesn't get worse.
By worse I mean so i don't have to replace this section of driveway