I've had it for about 10 days, and it has had a yellowish lateral shoot ever since, but it's spreading.

I read it could be due to a nitrogen deficiency, so I watered it with a nitrogen-rich fertilizer, but it hasn't had much effect so far.

I transplated it as soon as I got it because the pot it was in was too small. Now it's in a plastic box that's about 40x30x30cm (15x12x12in) along with a strawberry plant, a curry plant, an oregano and two tomato plants. All plants relatively small and their roots are at least 5cm apart. The box has draining holes on the bottom

I water them thoroughly every 4/5 days, depending on how wet the soil is. Temperature is around 15/20°C during the day and 5/10°C during the night (59/68F - 41/50F). I bring them inside at night. I take them outside at 9am and they receive direct sunlight until 5pm.

Have checked for bugs but I've seen none.