Why does my tomato plant look like it's dying?

My wife and I decided to start a garden to grow our own plants, among other things we did was to get one of those topsy turvy planters for a tomato plant, Over the last three weeks, it's been doing very well. I've been watering it once to twice daily until the water starts draining through the bottom of the planter, it gets plenty of sun, I've placed some eggshells, coffee grounds, and banana peels in the top for fertilizing purposes, and the stems are almost all thick and strong. Just yesterday, the mother of our soon to be neighbors was over working on their property and she said the plant is doing much better than her own, and she's been growing them for years. today, I went out to have a look at it and water it, and half of the leaves and stems have turned yellow. all of the yellow ones are the thinner ones, the thick main stems are fine, but the smaller ones have me worried. is there something I've done wrong with the plant, and is there anything I can do to undo any damage?