I'm having upper front tooth pain, but no fracture/decay/anything. any ideas?

Non-vital nerve: This is only a guess. Without evaluating the tooth personally and examining a radiograph, it is impossible to tell. You may have traumatized it years ago and now the non-vital nerve is causing problems. It can also be your bite. See a local dentist for a definitive diagnosis.

See your dentist: Has your tooth changed color? Sometimes it is not easy for the patient to know what is going on in their mouth without a professional advise. It will be best to have a dentist take a look at this before something else happens.

Could be a fracture: Depending upon the history- trauma, grinding, etc., there could be a minor fracture or the nerve (the pulp) could be dying or is already dead inside the tooth. Is the tooth discoloring at all. Dopes it hurt to touch, eating, or temperatures. See a dentist asap for an x-ray and evaluation.

See Endodontist: Endodontists are dentists who specialize in saving teeth, and have at least 2-3 years of advanced training in root canals. They are experts at diagnosing tooth pain and use advanced special equipment to treat patients efficiently and comfortably.