4 weeks after section, incision is suddenly hurting

KMLP

Just asked this question over on my BMB, and then I remembered this board was here. 

I was feeling really good and hardly having any tenderness, then bam, my incision is killing me.  It is especially on my left side.  I can't think of anything I did that would have aggravated it.  It's so tender that I can hardly stand to get up and down and I can't have any clothing touching it.  WTH?