Right breast and arm feels numb/weak. Both heats up to the point it feels cold. Right hand as well followed by tingles. Lower back. Any ideas/causes?

Depends on details. Pay careful attention to what part of right arm and breast are numb. "Heats up toe the point it feels cold" may be autonomic dysfunction. Pay attention to specifically what part of arm tingles. If low back is related then combination of arm and low back in setting of otherwise healthy young woman may mean stress biology (in which case tests probably normal). Quite treatable after diagnosis.