First, at 4 weeks, it may just be time for the very first leaves to die out, but not usually. You need to tell us what kind of soil you're using. Do you know it's ph? If not, you need to. At 4 weeks, in a pot that small, it could be running out of nutrients, particularly, nitrogen, though this may not be the case. Get a good all around fertilizer with NPK & all necessary micro nutrients, that is approved for foliar feeding, and give her a spray to both sides of the leaves when the room temp is below 80 degrees, and, following the manufacturer's guidelines, give some to the soil, too, but, make sure you're using a water soluble fert. Are you leaving any windows opened that could be allowing pests, like the six spotted leaf hopper, into your house? It's kind of hard to diagnose these things from a distance, but the foliar spray with a complete fert should stop the problem, unless it's insect related. But, if the soil's ph is off, it'll return.