Looks like you may have a couple of snails or slugs in that pot - they come out in the dark and hide during the day. Organic slug bait will do the trick.
The odd yellow leaf is not unusual for a new plant. Don't forget these plants have often been raised in a greenhouse with ample humidity, and luxury care in the way of feeding and watering. Btw, are you giving it a little bit of dilute fertilizer?
