Why do I still have swelling after wisdom tooth removal?

I'm in my 20s and I had all 4 of my impacted wisdom teeth removed surgically 2 months ago by an oral surgeon. 2 weeks after, I had gotten an abscess infection in one of my lower jaw extraction sites. I went back and the surgeon did an i&is and cleaned the area surgically. it's been one month & still have some swelling in the area the tissue feels a little hard on my jaw. i went back to the surgeon for a one mont check up and he did an xray and said doesn't know why. I would like some feedback.