This is a good question. It is very important for you to make an appointment with your primary care doctor
to discuss your symptoms and have a full history and physical. Depending on what your doctor discovers during your exam, he or she may refer you to a dermatologist
for further evaluation. It is possible that you have an infection or abscess
on the skin underneath your breast. This would cause pain and cause it to feel hot. However, it would be unusual for it to fester for a few months without causing further problems such as fever. It is also possible that you have candidiasis, or a yeast infection, under your breast. This commonly occurs under pendulous breasts as it is a warm, dark place where yeast can thrive. This would have started out as a reddish rash with white discharge. If it is not treated the skin can become darkened over time. Although very unusual, certain types of breast cancer can present with skin changes and pain so your doctor may order imaging to rule this out. Again, it is very important that you seek medical care as soon as possible so that you can receive a correct diagnosis and appropriate treatment.