Not sure I had acne, but I got really painful spots on my jawline, upper lip and esp forehead. I tracked it back to starting to drink a daily latte after I had DS. I had always been a tea drinker (with a splash of milk) until then.
I did a bit of research on the internet, and lots of foods seems cause spots in different people. As coffee, and large quantities of milk, was the only change to my diet, it was pretty easy to identify milk as the trigger. I swapped it for soya milk, and the effect was almost instant. The spots ached less, and within a week I would say, the spots were gone.
My skin isn't totally clear, I get the odd spot every couple of months now, but ten times better than when I was drinking milk.
Up until then I didn't think that what I ate could affect my skin so much. I'm a lot more careful about what I eat now.
As I said I'm not sure I had acne, and I know that for lots of people it's not about diet, but my spots were def diet related.
Good luck in trying to find what trigger your acne, I know how terrible it makes you feel.