Try using the IRS webpage linked below to access a transcript (abbreviated version) of your 2017 return. On this transcript, you'll find your 2017 AGI and should be able to complete your e-filing.
Here's another option:
Did you use Online TurboTax last year for 2017? If so, and if you are in the same account, log in and at the Tax Home go to the section "Your Tax Returns & Documents". Expand that section and choose tax year 2017. There should be a free link "View adjusted gross income (AGI.)"
Was that successful? If you found no evidence of a 2017 online TurboTax return, you may have multiple accounts.
What did you mean by "I have no access to my last year's AGI"? Does that mean you didn't use TurboTax for 2017? Or did it mean that you are unable to find the account with your 2017 online TurboTax return? Or do you find it, but it says access is locked until you pay? I assume if you are military E1-E5 you are getting a free 2018 Deluxe return, so don't pay anything. Instead report back for more troubleshooting.