I have a mint plant that isn't doing very well. I bought it in a grocery store two days ago, and it's been living inside by a window ever since. There's also some fluorescent lighting that's on a lot. The problem is that leaves near the bottom of the plant have been turning brown and falling off. I've also noticed some tiny black specks around little brown spots on the leaves, and a few odd white spots. Anyone know what the problem might be?