I have been using 5 mg of Ambien for 4 weeks. Is it early enough that I can just stop taking it?

Yes, it is early enough to stop. Try not to be on it for too long. I’ve been on it 20 years now and trying to wean off and teach the body to sleep without it is very hard.

I suggest you speak with your Dr. if you decide to discontinue the use of this hipnotic/sedative.
Also to become dependent to Zolpidem, the active ingredient of Ambien it varies from person to person, everyone's metabolism reacts differently to the drug, it can be easier for some people than other, still, if you believe you can manage your insomnia without a sleeping aid and have less chemicals in your system that would be beneficial for you, some people can other people need medications depending on how serious/severe any condition they may have is.
Whatever you decide it is always best to consult with a medical professional first.