Q: New iPhone and Messages isn't connecting to my group chats!

I got a new iPhone and now my group messages won't connect to Messages! One-on-one messages connect but not my group messages! My group of friends and I text all the time in our group chat, and after I switched my iPhone 4S to my new iPhone 6, the group conversations don't connect to Messages! But, my one-on-one convos do?? Why??? Help!