[Adriftpanda]

Depending on what you have to work, assuming you're still working out at home, back extensions is a great lower back exercise. Lay on your stomach. Something elevated, maybe a bed or couch, and slide yourself down to the edge of whatever you're using, bed or couch. Make sure your hips are still on the bed. Your lower body should be on and your upper body should be hanging off.

Keeping your body and back straight, slowly bend down and up. You can place your hands behind your head when doing this or just across your chest.

Sorry if I didn't explain this well enough.

Also, glad to hear you're getting in shape. For me, the biggest thing about getting in shape was to understand nutrition but that's a whole different topic for another time. I always tell my friends, before I can train them they have to understand proper nutrition. I can give them all the exercise to do but without proper understanding of nutrition, it's pointless.