First and foremost it sounds like the two of you need to sit down and have a discussion on how you communicate. This is not to say that you don't communicate now, but BDSM often requires a more sophisticated language.
I often say "no, don't!" to J when we play, or try to push his hands away. In the heat of the moment it's fun to resist and to be forced, it's fun to have my limits challenged and pushed. All around good times for both of us.
But, there is a HUGE difference between this and not being able to stop a scene when I am truly in distress or have hit as far as I can go. That's the point where a speceific, designated safe word gets used. There is no confusion as to what is the scene and what is a legitimate safety concern/limit.
If this is clear between the two of you yet your Master chooses to disregard it, that's a major red flag.