Hey! Maybe try changing your password, but if this issue has been occurring for this long, maybe try contacting a staff member for some help. Make sure then when the webpage is up, it’s not minimized in the background.
Just checking, but you are seeing this login page after you submit your login details, right?
(https://i.imgur.com/2cI1ljK.png)
Usually it takes a few minutes of being logged into the login page to be able to login and connect to the game itself for some people. If you're not seeing this page then the login details you are typing in are incorrect. If you are definitely seeing this login page, then we can be reassured that your login details really are correct thus no password change should be necessary.
If this is the case then you may need to re-consider if your connection is working efficiently. Have you attempted to restart your router? It may be the case that you can use your browser and whatnot, but it takes more strength in connection for the game. Not a dramatic amount of strength, but it just takes more umpth. Especially if you're using a wireless connection. If you are then I would consider getting an ethernet cable so you are getting your wifi connection directly rather than wirelessly to get that strong connection, if you are using wireless connection.
Changes such as internet providers could also be a reason for your sudden inability to log into the game, if any change of internet provider has been made. Either way, you should consider what I said above.