I’ve been buying mine from Amazon for the last few years. One notch after exposure has been being used by many of us on another forum. If sick, one notch followed by another in 12-24 hours and most people have recovered by the 2nd day. This is just word of mouth experience, including with myself, and not actual medical advice. Your mileage may vary.
Friends that prefer pills use All Day Chemist- https://www.alldaychemist.com/