Almost every report in QuickBooks Online (QBO) can be run with a custom date range for whichever months you need, see the steps below to learn how:
Running a Report For Any Month in 2018
From QuickBooks Online, navigate to the Reports tab and search for whichever report you need in the search bar. Click the result in the pane below to open the report.
Select the Report period drop-down and click Custom. Enter the month's time frame in the boxes that appear. For example, to view December's information, enter 12/01/2018 to 12/31/2018.
Click Run Report to view that month's information.
I'm attaching a short video example of this process for your convenience:
Doing this will enable you to run all the 2018 monthly reports you need. Check out this detailed guide on the available reports in QuickBooks Online for more information. Please reach out to me here should you have any additional questions or concerns. Thanks for coming to the Community, wishing you and your business continued success.