Sorry to hear about the losses of your bees. That's very disconcerting.

I'm not a beekeeper but I know that most counties have a Beekeeper Association. It's a good idea to join one or, at least, visit such a group for local advice. Members are often eager to help new beekeepers.

It looks like your bee population got too low to sustain the cluster. If you never tested for or treated for Varroa Mites, its possible the colony succumbed to them. If Varroa was present, it probably had the hive under stress last Fall, and then as you had the normal attrition of bees during the Winter the colony wasn't strong enough to hold the cluster in cold weather.