Believe it or not, it is a complete myth that acne
breakouts are associated with the diet. None of the various culprits that are commonly believed to be associated with acne (greasy food, soda, chocolate) actually have any affect whatsoever on acne flares.
Therefore, you will need to look elsewhere for the explanation. Since acne is caused by clogging of the pores with dead skin, bacteria, sweat, and other debris, the most likely explanation is that you have somehow done something recently to increase pore clogging. If the acne is mostly on your neck, one explanation could be, for example, if you have recently started exercising and working out more (causing increased sweating). There are also certain medications that can be associated with acne flares, so if you have recently started a new medication that might be the cause.
Regardless, it sounds like you need to put a skin care program in place to help control the acne. If regular skin cleaning and exfoliation, with the addition of over the counter acne preparations, does not work for you, then you will want to set up an appointment with either a dermatologist
or your primary care doctor
. They can help you decide if stronger medications are needed for your acne.