Open enrollment for 2019 health plans ends December 15, 2018 in most states. Make sure to re-enroll, pick a new plan, enroll in a plan, and/or verify your plan and cost assistance by then.
Although extension may be granted on a federal and/or state level, and although some states have extended open enrollment already, it is a good idea to make sure you have logged into the marketplace website and verified everything before open enrollment ends.
The simplest way to check everything is in order is to go to HealthCare.Gov.
For more details, see Open Enrollment 2019.