I have a big bump under my tongue and red rash is...

Treatment : 
Treatment depends on the cause, so a medical examination must be performed and a specialist consulted. For treatment, we recommend paying attention to oral and dental hygiene, and drinking fluids in sufficient quantities. In the event of a bacterial infection, the antibiotic Amoxicillin 500 mg is used twice a day in addition to Metronidazole 500 mg 3 times a day for a week, and in If the cause is oral fungi, Miconazole ointment is used twice daily ,and for pain you can use Ibuprofen 600mg  times daily 
Diagnosis : 
By taking the medical history, doing a clinical examination, doing a blood test (CBC) to detect infections, examining the salivary glands, and taking a biopsy of the swelling.
Causes : 
Poor oral and dental hygiene
Gingivitis
blockage of salivary ducts
Inflammation of the glands in the mouth
Advice : 
you should visit the Dentist to get proper managment