Have you updated the apn settings to cricket's ?

I am only able to send single text messages from my Samsung Mega phone. I have cricket service, but transferred from AT&T. This problem only surfaced in the last week but is very inconvenient because I use this phone for work. Any suggestions? There is not problem with text messages sent to more than one person (even just to two). Also, what is the message center number for my phone? Should my own phone number be there?