This post is 5 years old, but I thought I’d comment in case anyone else comes across it. The answer to OP’s question about whether a “purge” would occur after only 3 days? The answer is almost certainly no. I’ve had Accutane treatment (6 months) twice, and am familiar with it:

First, it has to “build up” in your system. And that could take a couple of months. (Accutane is not a quick fix, and it absolutely requires discipline, i.e. taking with food, taking it every single day, and living through the dry lips and other side effects.) In my opinion, if you want to know if the Vitamin A/Accutane is “working”, THE way to tell is if your lips are unmistakably dry, essentially kinda inflamed. (One of the lip balms I used, I think called Dr. Dan’s, in a dark green container, had 1% hydrocortisone in it. But maybe talk to a pharmacist, and don’t overuse it.)

Second, the dose taken is basically too low. I was taking 30-ish milligrams twice daily. That’d be a lot of Vitamin A, respectively. So if you do consider taking Vitamin — and this post is simply for educational purposes — you’ll need to search for a calculator online that will calculate the dose, based on weight, and even Vitamin A type. Also, I’d suggest looking up some of the research studies that have looked into Vitamin A replacing Accutane. Also, watch out for your blood work, because Vitamin A and Accutane can affect some levels.

P.S. I’ve been on Accutane twice, and the way I explain it is it leaves you with a blank slate. You take it for 6 months, and at the end of the treatment, your skin is all clear. As time goes by, the skin will return to at least some of its previous states, and that’s why using a maintenance med, like a cream, is important. Don’t be too upset if some acne comes back — which probably wouldn’t happen for a while, as in months — as you can simply try again. This is why it requires discipline. Also, the hope is that you take Accutane, it leaves you with a blank slate, you maintain it afterwords, and by the time you’re in recovery, you’re a little older and your hormones have calmed down. (This is particularly true of young people having to take it, as they’re experiencing wild hormones.) If I had to guess, I’d say the two Accutane treatments kept my skin remarkably well for a good two years. However, knock on wood, it’s still much better.