lost my notes

Notes can be syncing from multiple email accounts such as yahoo, gmail, outlook...

Have you recently removed any mail accounts?

Try by checking your settings:

1. In the Settings app, tap Mail.
2. Tap Accounts, then tap each email account that you want to check.
3. Make sure Notes is turned on.

Please see this: If you're missing notes on your iPhone, iPad or iPod touch – Apple Support (UK)