I am a 27 yr old female i just had a lung scan and i was perfect i have had post nasal drip for a month now i'm spitting up little specs of blood?

Could be allergy: It could be allergy problem, but there's could be other more serous problem, such as cancer, bleeding disorder or liver problem. If symptom persist you should see a doctor to get a check up.

Need a complete exam: Spitting up blood is not normal. You might have a sinus or chest infection that is causing the problem. If this persists, you really need to be examined and have an endocscopy (light that goes in the throat)_ to see where the prblem might be. Rarely, you could have a growth causing the problem. Please do not ignore this symptom.