Differin acne product made my skin worsen??

So I’m currently 18 and I’ve had acne for around 4/5 years now. My acne on my face over these years have constantly changed position: when I was 14 it was mainly on my forehead and chin and cheeks and now it’s mainly on my cheeks and a few on my forehead.
I’ve been to the doctors numerous times to ask for medication to clear my acne and I’ve tried SOO many over the counter products but nothing seems to work. I’ve tried even using a simplistic routine by just washing my face with Simple face wash and still nothing happened. I even tried going natural for a bit and nope nothing worked.

I then began to do my own research and discovered that retinoids have very positive results.
The doctor prescribed my Differin 1% in January and I’ve been using it for 5 days a week since.
Now I’m 100% sure I’ve been using this correctly because I’ve watched hundreds of videos on it: pea size amount, only on dry skin after washing face not in sunlight only at night etc.

Ik it’s only been a month, my cheeks are showing pretty positive results. Even though I am purging, I can see that the general texture on my cheeks are better and the spots are going down.
HOWEVER, my forehead seems to have formed SO many more little spots everywhere?? They’re not whiteheads but so many closed comodomes on my forehead all of a sudden? It can’t be an allergic reaction as if it were, it’d be the same case for my cheeks?!

But I’m just worried as my forehead acne is making me demotivated to continue Differin. I really want my skin to be clear before I start university in October. Though it’s only been a month since I started Differin, I don’t know why my forehead has gone like that??

BTW, I use a Simple face wash to remove any dirt/makeup from my skin and then I use a Neutrogena 2% salicylic acid face wash. I wait for my skin to dry and then apply the pea size amount of differin. Then I use ‘aveeno (for very very dry skin)’.

Pls help