Hello Thanks for query . A painless lump on the scrotal sac could be mostly a Sebaceous Cyst . The scrotal skin is rich in sebaceous glands and hence prone to get more sebaceous cyst due to accumulation of sebum beneath the skin. Normally they fade away without treatment however they need to be treated if increase in size or get infected. Take broad spectrum antibiotic like Augmentin along with anti inflammatory drug like Diclofenac twice daily. If does not subside within a week you will need to consult qualified General Surgeon for clinical examination to confirm the diagnosis and further treatment. If needed he may advise you to get it excised in Toto (Completely along with the sac) . Dr.Patil.