Why camera is showing insert sd again error

You need to buy a new card, the one you currently have is faulty.

You may disconnect it to your computer via the Reader and run a memory card recovery freeware to save your data inside it and format this card to see whether it could work. (This freeware had recovered 90% of my important data when Smartphone memory card received the "not formatted error" message. You could try it to take a chance. )
Tips:
1. Do not store any new data on this card in case of the original data overwritten by new data.
2. Do not save the recovered data on the same card in case of recovery failure.
3. Format this card to see whether it could work as before. However, in my opinion, buying a new memory card can be the best choice for you.
4. Do not forget to back up your important data regularly in the future.