It sounds like you're entering the wrong password in the login field.
Since you're logged in right now, you can change your password to something you can remember. Do that by clicking on the person icon in the navbar, then click on "Settings" and at the bottom of that page, click on "Change your E-Mail or password".
Now change your password to something you can remember, and be sure to save your changes on that page. Next time you need to login you should be able to do it. Just make sure you enter both your username and password correctly.
