Sensitivity to rejection is NOT a symptom of ADHD, but is associated with any history of repeated rejection. ADHD just happens to be one common cause of rejection since disorganisation and distractibility lead to forgetfulness and screw-ups.
Could you have ADHD? Sure. But then your difficulties could be due to a number of things. If you want to get to the bottom of it, see a qualified clinician, such as a clinical psychologist.