First hard cider is fermenting for eternity

This is my first attempt. I used 5 gallons of apple juice and 2lbs of brown sugar. Pitched S05 3 weeks ago and the airlock is still going about every 10-15 seconds. I've only done beer before and visable fermentation was usually done by 5-6 days. I was planning on leaving this in primary for a month, but that might not be enough if the fermentation doesn't stop. Is this normal? How long do any experts think it should be going? It started at 1.07, which is what I wanted. I need it to be done fermenting because I'm bottle conditioning about half of it. (experimenting with the other half with back sweetening and adding different flavors, so I'm not worried about it being too dry) Any tips? Or am I being impatient?

Whats your gravity? Thats the only way to know if it is still fermenting.

Slow is good for cider. What temp are you fermenting at?

temp is a steady 65. is that too low? I haven't taken a hydrometer reading since I started. I generally only do that once airlock activity has stopped. Should I check it for a few days in a row?

65* is nice. My batches, which start around 1.060, often take 3+ weeks to ferment to dry. A couple of well spaced readings should give a better idea of where you're at and how fast the batch is going.