I have very bad acne mainly on my forehead and it has been this way since I was about 11 years old (I'm 16). I was diagnosed with Hypothyroidism when I was 7 and from that pointon I developed a few pimples every now and then. Then when I was 14 I was diagnosed with Hashimoto's disease as well and my acne has gotten worse. I eat a healthy gluten free and dairy free diet, get enough sleep, drink lots of water, and exercise regularly so the only thing I can guess it is caused by is the thyroid problems I have but at the same time anyone I know with similar thyroid problems doesn't have acne.
Probably not causing acne directly, but increased levels of thyroid hormone (either from disease itself or from higher dose of levothyroxine pill) can cause stress- like state which in turn can cause or worsen acne.
You may also discuss this with your endocrinologist.
Best!
Vise