Mama, I know how scary this is, please don't wait, go back to your pedia or go to the hospital na ngayon if it's getting bigger or your baby's fever goes up. Perianal issues in babies need proper monitoring, especially kung lumalaki pa rin kahit on antibiotics na.
Your pedia's right to have a plan ready kung kailangan ng surgeon, that's good care. A few of my mum friends have had little ones with similar concerns, and ang best thing talaga is to follow through with the specialist kung recommended. The crying during bowel movements is heartbreaking, I get it, but you're doing the right thing by getting medical help.
Keep an eye on his temperature, appetite, at activity level din. Hang in there, Mama, you've got this.