Cara - The symptoms shown in the photos are generic, meaning they can have several possible causes. The most likely causes are root damage from repotting, improper watering and inadequate light. (When posting photos it is best to post a photo that shows the entire plant because that reveals much more.)
You must provide better light than the northeast window. If you are seeing insects, especially flying gnats, then that is due to the quality of the soil used by the farmer's market. Gnats are also a sign of soil that is kept too moist. Once a plant is repotted, all bets are off about watering instructions because we don't know how much soil was added, where it was added and just how the repotting was done. No doubt soil was added to the top of the original rootball. If so, remove all loose soil that is not in immediate contact with roots. Removing that excess soil will help the soil below dry out more readily and it will also eliminate some of the gnat larvae that inhabit the upper levels of the soil.
In sum, more light, less soil and less water.
