it is so early in the plants life that unless the soil is really outta wack(preferted or high or low ph) you probably just got a bad plant. all seeds are not equal. it could have some kind of defect. i would try germing some more seeds. if that plant is still on it's 1st 2 leaves at three weeks it has something seriously wrong and will probably never be a really healthy plant. kinda sucks but at least you didn't spend months on it. good luck!