Whilst I'm sure chocolate in itself doesn't cause pimples, bad diet and junk food makes your entire body unhealthy, including your skin.
Try eating home-cooked meals made from scratch. I read this book called "Healthy Living" by Michio Kushi and it helped me to see that the decline in health in the recent Western world is due in large part to processed foods.
If weight loss is not a factor (i.e. you are at your ideal weight), try making the "junk food" that you crave at home from whole ingredients.
Your skin will use all the nutrients in the food you eat to regenerate.
Also, try drinking fresh juice. I drink carrot juice every morning (i used to hate the taste but i'm getting used too it.)
I also think it's important to match the severity of acne with the level of medication taken. Try not to self-diagnose, go to the doctor and ask.
If you only have very mild acne or pimples then an over the counter medication may be adequate. If it is more severe, recognise this and treat it right away without wasting money on ineffective solutions and putting excess chemicals in your body.
I am of the opinion that if you treat the acne, and then use only natural, fragrance free products on your skin, your skin will stay healthy.
I went on Diane 35 ED for three months and my skin cleared up completely. Now i use mild cleanser (Angels on Bare Skin from Lush) and Cetaphil moisturiser.
...Wow, that was really long.