I always have runny nose and sometimes I feel something dripping down my throat. What does this mean?

Allergies. This may be related to allergies. Allergies can be "seasonal" or "perennial." the runny nose may also be chronic sinusitis. Nasal steroids and/or nasal antihistamines are very effective for this.
Allergy. If you have chronic persistent runny nose and post nasal dripping as you say, it is most likely an allergy. Colds and upper respiratory symptoms should subside by 1-2 weeks at the most.