If it was newly potted right after purchasing and that timing coincided with the rainy spell, it may be your tree is exhibiting "transplant shock" (and not rain issues) and will snap out of it in a couple days. I have a very young 'Bloodgood' JM in a very large pot under the dappled shade of some very tall trees. It started out as a 2½' sapling that is now 3-4 years old and about 4' tall above the dirt line in its pot. It seems to be happy where it 'lives' and gets automatic water sprinkling every 3 days. I did put a bamboo stake on it the first year I had it, mostly to protect the tiny thing from any leaning that might result from any wind events. I think I removed the stake in year 2. Rain never bothers mine, and Texas has had some torrential rains more than once during this tree's first few years, especially this past spring, which moved on to cause some severe flooding in adjacent states:
