Dog losing hair

Sarah • 22
I know this isn't really what <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> is for but I was just wondering if any of you dog owners have any idea why my dog is losing all her hair. We noticed it about a month ago on her neck and thought it was from her collar. Since we noticed it we have kept her collar off but we have started to notice she is thinning out other places as well. We haven't changed her food in a long time. She is only 2 years old. Any ideas??