Could the drastic weather changes have an effect on them and their intake of sugar water?
Absolutely. Feeding with an inverted jar over the inner cover is the best way to go in my opinion. However, the bees can only raise as much brood as they can keep warm. I would highly suggest closing of the SBB to help retain the heat so the bees can raise more brood. If you continue to have cool weather, feeding a quart of warm syrup in the morning will be taken better than leaving a gallon of cold syrup for them. Depending on the amount of the bees and the size hive you have then in, you may want to reduce their area. Try not to give them anymore room then they can fill right now. Don't forget, the colony will be in decline for the next 30 days or so until brood starts to hatch.
Welcome to the forum, it is great to have young beekeepers