Hi- I Am A 25 Year Old Girl Who Is

Hi- I am a 25 year old girl who is suffering from an intermittent rash. It started in August around the sixth and lasted until the first weekend in September. Since then it seems to reappear foe 4-5 days every two to three weeks. It starts at my bra line and extends to my lower abdomen. But is always itchiest on my ribs. I have not changed any soaps or beauty products. Every week I eat variations on the same things. Green veggies, eggs, meat, fish, almonds and the occasional (1 a week or so) quest bar. This doesn't change ever. I go to yoga once or twice a week and the gym once or twice a week. Any advice on how to stop it??