As long as you're using a paid TurboTax product, you should be able to find your tax returns filed using the same account (same username and password). In order to access a tax return, you must log in using the EXACT account that you used when filing. Many users have multiple accounts without realizing it. See the info below for determining if you have more than one TT account.
https://ttlc.intuit.com/community/account-management/help/how-many-turbotax-accounts-do-i-have/01/26133
Additionally, if you used the Free Edition when filing, your access to your TurboTax Online returns is limited by time. See the TurboTax FAQ below for more info.
https://ttlc.intuit.com/community/my-tax-return/help/how-long-will-i-be-able-to-access-my-turbotax-online-return-from-your-server/01/26600