In the spring the queen will start laying with a passion, and in good weather will lay more eggs than is able for the amount of nurse bees within the hive to take care of when they turn into lava if the weather turns off colder. Wow, that was a mouthful huh? Sometimes the queen lays more than the number of nurse bees can take care of if the weather turns cooler. Was that better?
I don't know if this is the case with yours, but you mentioned the weather has turned rainy?
I've been keeping a few hives for the past 20-25 years, and no longer treatment free as I got tired of the losses.