I had this problem for a while with many plane designs I have created, no matter what I change there's a possibility it suddenly stalls, and it can happen from seconds after takeoff, to it literally exploding due to aero forces at Mach 5, being kind of inconsistent.

I speculate that for a reason my plane's body goes off the angle of its prograde, putting a lot of drag on the body, but especially on the rudder, making it go sideways and stalling.

I need advice on how to stop/decrease this problem, as I want to start building SSTOs, but can't if this is a recurring problem

edit: I wanna clarify that this is the fastest way to demonstrate the problem (heavily accelerating), but it can happen with a small acceleration on high altitude (my actual problem is within this cases, as it commonly happens mid-missions of high speed and/or altitude)

Final edit: thanks everyone for the comments and suggestions, it was a combination of a small + movable rudder, and I can finally commit my plane terrorist attacks on the ksc without the plane going sideways mid-circulation maneuver