I have a bruise like place in my armpit. it doesn't hurt and it hasn't gone away in the few months i've known it was there. what could cause this?

Need to examine: It is not feasible to provide a meaningful opinion without taking additional history, and physical examination, however, it does not appear to be a serious issue. You may watch and wait. If the lesion gets bitter, it ulcerates, or discharge develops or more lesions appear, see a doctor. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex. Get HPV vaccine