Hello Though Thorough history and clinical evaluation is required to comment .Still I could help you by this. If swelling is at floor of the mouth (beneath the tongue) and soft then it is suggestive of ranula and if the swelling gives pain and increases on eating then it is suggestive of sialolithiasis (Stone in salivary gland or duct).in both the cases you need to get surgical treatment done by an oral and maxillofacial surgeon.