2004 Honda Pilot key sticks in lock

2004 Honda Pilot 40000 miles

I don't have keyless entry on my Pilot and have to insert the key into the lock to unlock the car. In the last few months, the key has been sticking in the lock and it won't let my unlock the driver's side door. The key slot in the rear of the car is beginning to stick as well. The passenger side door is fine though. Any idea why this is happening and how I can fix it? Thanks