Without a photo, impossible to tell. Even with a photo, it might be hard. But the most common and likely problems are too little moisture (either underwatering or dry air - very common in Minnesota in winter) and too much salt build-up from over-fertilizing or from soft water. Read here:
Some things you can do: Pay careful attention to the moister level in the pot - water meters are cheap and useful. Mist the plant. Use only distilled water when watering. Hold off on the fertilizing for awhile.