Thanks for choosing health care magic for posting your query.
I have gone through your question in detail and I can understand what you are going through.
4 days is a long time for the vasectomy
to heal. If the lesion has become black and it is so much painful then painkillers alone wont help. You need to probably get a second opinion
for the same. Probably it has got infected and you will need culture and sensitivity of the suture area to determine the exact anti biotic.
Hope I am able to answer your concerns.
If you have any further query, I would be glad to help you. You just need to contact me on this below mentioned link:
Wish you good health,
Dr. Srikanth Reddy M.D.