Incredibly slow fermentation

I pitched some champagne yeast into my cider on the 21st of February. Now it's bubbling, but VERY slowly - about one bubble through the airlock every minute or minute and a half. The hydrometer reading hasn't changed at all...
The temperature is ranges from 60-70 degrees. I live in southern CA, and the temps here are 70 high in the day, and 50 low in the night, but the house usually doesn't go below 60.

Should I pitch more yeast? Is it not fermenting fast enough? Should I make it warmer/colder?
Thanks!

Yeast might be stressed from the temp swings. Rather than higher or lower, try getting it somewhere where the temp is more stable. A closet usually doesn't swing up and down as much as the rest of the house.

If you used store bought juice have you checked the ingredient list for preservatives?

Living in Northern Florida where the temp swings wildly in all seasons except for summer, I switched to using Nottingham exclusively for all cider making. It holds a steady fermentation even through 10 degree temperature shifts in the brewing closet. I've gotten stuck fermentation with both Montrachet and Wyeast stuff in the same conditions, with beer. Pitched Nottingham into stuck fermentation and it lit off within 24 hours everytime. I've only ever used strictly Nottingham with cider so I don't know if you'd get off flavors from a yeast switch.

I'm certain that others will call me a barbarian or Bubba for doing things like that, but it works every time for me.