Posture related breathing problems. I'm unable to exhale fully and don't know if its asthma, airway remodeling, allergies, or something else.?

No. That is a common and overrated opinion about bad posturing. The only known posture related breathing restriction is related to rotoscoliosis or abnormal bending and rotation of the back bone -- most 'bad' posture is not caused by rotoscoliosis but more from lack of fitness and obesity.