Hi katienika2019,
Welcome to the Apple community where some of us do our best to help each other.
Apple has a support article that can help troubleshoot, and with tips to follow:
If you can't sign in to iMessages on your iPhone, iPad, or iPod touch
https://support.apple.com/en-au/HT204065
General info on using messages:
https://support.apple.com/en-au/HT201287
If you changed your Apple ID or password lately:
Might be worth also checking out this article ...
What to do after you change your Apple ID or password
https://support.apple.com/en-us/HT204071
Hope something here will help you enjoy using Messages again.
Else there is a "Get Support" link to Apple, at top right of this page, (not sure if it will work ok in your country)
Cheers