Welcome to HealthcareMagic. It looks like a small hematoma
breast which has formed after trauma to the area . Apply warm compresses and some topical antiseptics. Also wear loose-fitting cotton clothing and use an antibacterial soap or mild soap like dove. You can also apply topical antibiotic
creams. However if the symptoms persist then oral anti inflammatory drugs may be needed. You have to consult your dermatologist
Hope it helps you. Regards.