Phone only sends as text and not as iMessage
I have an iPhone 4 and for the past couple days iMessage has been giving me a lot of problems. After fixing the whole "waiting for activation error", I am having problems with my messages being sent only as text messages and not as iMessages. I have iMessage enabled and my phone number is under the send & receive thing. For example, my messages in groupchats are sent as text messages and each one of the other members receives my messages individually. Can someone please help me with this? I've already tried resetting network settings, setting up my phone as new, etc etc.
Thanks!
iPhone 4, iOS 7.1