Hello Thanks for query . A brown lump on scrotal sac which swelled up recently is most likely to be a Infected Sebaceous Cyst . The scrotal skin is rich in sebaceous glands and hence prone to get sebaceous cyst due to accumulation of sebum beneath the skin. Normally it fades away without treatment however needs to be treated if increase in size or get infected. Take antibiotics like Doxicycline and anti inflammatory medication like Diclofenac twice daily for a week . If does not subside consult qualified General Surgeon for clinical evaluation .You may need to get it excised in Toto under local anesthesia . Dr.Patil.