I keep getting a message that I need to sign on at least twice a day

being asked for a password is usually something outside of Thunderbird causing the connection to fail. Failure to connect means Thunderbird assume your password is at fault and prompts for it again. IF simply reentering it in the password dialog fixes the issue you might be having internet connectivity issues. If you are asked to re-authenticate with a webpage it may be security software you have like a VPN causing issues with your mail provider. Google for instance challenges often for those that have a VPN.