Hi, do not feel embarrassed - you're in a safe place where people do not judge anyone โค๏ธ
Before I start, can I ask you how long have you been using Differin? If you started to use differin in less than 12 weeks, it might be purging.
As an esthetician - when you tell me that your acne is mostly around chin/mouth area I would connect it with - maskne and cystic acne probably related to hormones. I do not like to use face map for mapping acne, but what I would recommend:
1. Go to dermatologist, a good dermatologist should ask you to do all the basic stuff like blood test, checking thyroid function
2. Go to gynecologist - cystic acne can be related to hormone inbalance, in some countries you won't be able to get hormone tests without a visit at gynecologist office.
3. If all tests are okay - allergic tests can be good too, I would also look at the diet - glycemic index if might also have a meaning to your skin, especially if you eat lots of processed food, milk, chocolate, etc. Is your life very stressful? Stress can also be related to acne.
Dermatologist can suggest you accutane (they usually suggest using accutane for cystic acne, if this acne is related to hormones then pills to balance hormones can do almost entire work), I guess retinoids can be also good thing, but you have to expect that first 3 months can be worse due to purging.
What you can do at this moment on your own - try Benton Snail Bee series if you're not allergic to bees, this series helped a lots of people with acne.
Still, I wish you all the best in your skincare journey โค๏ธ