I imagine it is indeed the rain. Excessive rainfall clogs up the roots with water and interferes with nitrogen uptake. It will get better as it dries out and is able to suck up some nitrogen again. You can put it in a container if you want to. I like them more in the ground, but I can see where you might want to keep it in a container for a while until you see how the soil drains and what the patterns of sunlight/shade are at your new place before you decide which plants will go in which place. I move coneflowers as needed with no negative repercussions.