Hello,
It can be due to an allergic reaction but since the blisters are painful as well, infections should be ruled out. Apply warm compresses, Neosporin ointment and calamine lotion and avoid messing with it. You can take anti-inflammatory pain killers like ibuprofen or acetaminophen .If the lumps persist then it will be best to get it evaluated from a dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
It sounds like you are having an allergic reaction to the sutures to me. I would call and describe what you are seeing to the surgeon on call for your surgeon's group. It is probably not an emergency, but they expect to hear from you if there are even minor complications.