I don't want to scare you, but if it is pretty constant you should have it checked.
My sister had a constant runny nose. She said she would just go through a box of tissues in no time. I kind of thought that she was exaggerating.
It turns out that she literally had an internal HOLE IN HER HEAD, and it was spinal fluid that was dripping out!!!!!
They told her that it was a miracle that they found it without her having a serious infection because that's how it is usually diagnosed. The surgery to repair it (via sinus) was actually quite minor in spite of how very, very serious it was.