Hi, You've gotten off to a great start. Sometimes wt loss slows down for no reason at all, then picks back up. But it's not as fast as the first week or two, when a lot of water leaves the body along with fat burning.
There are so many things that go into weight loss. It just isn't linear--there will be pauses and whooshes. The common definition of a plateau is one month with no wt loss. So you are not there, and probably don't need to do anything at all. If your calories go too low, your metabolism will slow down to conserve calories like nanahoney mentioned. It's counterintuitive but eating a little more calories can help the weight loss--everyone is different so you might need to tweak this to find you ideal zone. But even without upping the calories, your weight should start to drop again.
Btw it is not necessary to exercise to lose weight, though exercise is key in maintenance. It's a wonderfully healthy habit. But it just isn't necessary for weight loss.
Just keep ding what you're doing, maybe add in a little food. If you increase exercise too much while eating at a deficit, your body will turn to burning muscle for energy. Fitbit is based on averages, and we are all unique, so don't be afraid to veer from your Fitbit guidelines to find what works best for you.
Congratulations on your progress so far!