I went on to iMessage to text my sister and it said I have to re-sign in. I need to know A.S.A.P because this happens lots
I doubt that you have been hack. Most of the time iMessage ask me to resign in is when I swap out the SIM card, or when I lose connectivity for a long period of time, also if your carrier doing some maintenance on their equipment, it can reset the activation.
If your device is hacked remotely, it will not deactivate your iMessage, the only case I can think of iMessage been deactivate remotely is if the hacker have change your Apple ID password, in that case, you will not even be able to activate iMessage anymore unless you know the new password, only in that case I think you can consider the fact that someone is altering with your iMessage (Apple ID) account.
For more security, and if you have sever suspicion, you can change your iMessage activation password (Apple ID) as well as the recovery mail password (if you have linked a recovery mail to your Apple ID mail)