What Is Causing Stinging Pain In My Knuckle?

I pulled grass weeds in August, the grip was so strong to pull the weed, once pulled, the index finger at the knukle had a burning sensation. It's been hurting on-off ever since and especially at night. At the knukle of the index finger is more red and is slightly swollen. Sometimes a sting wakes me up at night. What have I done to both index fingers?