Try the 19/30 exercise: 19/30s exercise explained - View topic: Trumpet Herald forum
It will help you develop a relaxed open sound. I wonder if you are pinching your lips together. You do not need to do this to get the horn to speak. Your lips need to be close or together, but not PINCHED as this will constrain your sound.
Lastly, hook up with Jeanne Pocius: [email protected] and let her give you a Skype lessson. I would bet real money she can help you, and I will even offer to pay for half your lesson if you do it and tell her I sent you so I can pay her.