What causes a painful lump and pain in my lower gums?

Hello,

Welcome to icliniq.com.

By your description, it seems to be pericoronitis which is an infection caused just above the area where your wisdom tooth is erupting. This happens due to the pocket formed at the corner of the mouth where liquid and food debris seep into the erupting site causing inflammation and pain. The pain is felt in the jaw, ear, and below the jaw where you can palpate swollen lymph nodes. You should use warm salt water for gargling thrice daily and some painkillers till you visit your dentist. Either he will remove the wisdom tooth or will suggest a minor flap removal surgery according to your condition. I cannot say the exact treatment without seeing a picture of the area.

I hope this helps.

Thank you.