Apple Watch Activity Lost

My Apple Watch and Activity app on my phone would not sync. This is probably the fifth time this has happened since buying it in late December. A few times I have had success with turning my phone and Apple Watch off, turning airplane mode on and off, or repairing my Apple Watch. I did all three this time and none of my activity data is showing up on my watch or phone (for the second time). How do I get this data back? And how can I prevent losing data again?