iMessage on laptop and phone have totally de-synced.

I got a new MacBook Pro and everything set up perfectly except for iMessage. The texts on my phone and laptop are completely disconnected now. When I send a text from the computer, it sends from my email, and the recipient gets it in a new thread from whatever I sent last on my phone. I've gone into preferences and under "start new conversations from" it doesn't give me any choice but to use my Apple ID email. This never happened on my old Mac. My iMessages were completely synced on my computer and phone. Help?