Even though its been over a month it could still possibly be an irritation to the stitches. My little boy Pete had a little lump appear around a little black looking stitch somewhere around 2wks to a month after his surgery, I took him to the vet and they said it was completely normal and did nothing. 2 weeks after that it was still there and looked infected so I took him to my new vet (decided I didnt like that vet for many reasons) and he took him in the back and made a small incision and drained what appeared to be just a little puss from some irritation, after that it went away and hasnt been back since. The vet also told me that sometimes the dissolving stitches can take several months to fully dissolve. Good Luck
