I have a swollen painful bump under my arm which I think could be a swollen lymph node. I’ve had this before but this time it’s very sore?

Need to examine. What you described suggests an inflamed lymph node. Do you have any wound or injury on the hand or arm of the same side? It would be prudent to see your doctor for an evaluation as you may need antibiotic treatment. If you do no have access to a doctor, go the emergency room of a nearby hospital.
Wish you good health! - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form.
Practice safe sex, if you have sex.
Get HPV vaccine.