I brought my plant home a bit over 3 weeks ago, looking like this:

Very lush, erect leaves (though you can see a spot of brown on the edge of one in the front).

Now, my streptocarpus looks like this:

You can see the leaves are all droopy... Plus basically every leaf has a bit of brown on them, like so:

What is wrong with my plant? I have been watering it only when the soil is dry to the touch, as suggested for streptocarpus (so about 2x/week), and it has been sitting on my windowsill this whole time, next to a window that faces north (so no direct sun), and I make sure to keep my blinds open during the day. It is about 65-70 degrees indoors at all times.

Am I caring for the plant wrong? Does it have a disease? I thought there was a possible pest infestation at first, but I can't actually see any pests on it... I've release live ladybugs onto the plant this past week, just in case.

Everyone says streptocarpus is so easy to grow, but as a first-timer I'm experiencing a lot of frustration with this one!