Do a few gentle floor exercises. Kneel on the floor on all fours and arch your back up and down (like a cat) it always soothes my backache. Take ibuprofen as Sqad suggests.
Depends on severity. If you can move, then you should.
Again depends on how you have managed to injure yourself, but, possibly expect it to tighten up further as the day goes on and take pain releif (Ibuprofen)