Breast feeding

Is there a way to know if your losing your milk supply my baby is 3 weeks old she doubled her weight at her first appointment but we haven’t had an appointment for a week! I feel like I feed around the clock non stop! My boobs leak occasionally but are soft, she sometimes gets fussy while on the breast and unlatches! I’m not sure if it’s cause she fell off the nipple or if she’s just not getting what she wants( this has happened maybe 2-3 times)