My story is very similar to yours. 3c melonoma right arm. It was big and deep. During surgery they cut it out but also took surrounding tissue. They explained the scar would be bigger, but taking surrounding tissue they thought was best. I too had 2 lymph nodes takes out. 1 negative, and the other had microscopic melonoma cells. I started Keytruda a few weeks after surgery. Thankfully I have not had severe side effects. I was super tired at first, but getting less so after 3 infusions. I have a PET scan next week (3 month check) to check things out and confirm the Keytruda is working. Keep me posted on your next steps.