Welcome to the Healing Well Wrapped Club! The first few days are the toughest, and after that the first two weeks are the toughest...take it a day at a time.
Although your outsides don't seem to have gone through much--just 5 little slits, your insides have gone through a lot. You've had major surgery, and your stomach has been stretched and wrapped, then stitched, around your esophagus. It's been through a lot. At Day 6 you're still experiencing surgical pain.
Your wrap site is swelling, and no doubt the swelling is pulling on stitches. This swelling with continue to increase until it hits peak somewhere around 14 days. Then you're on the way toward gradual improvement. There are some rough days in the first 14, and those of us who've been through it know what you're dealing with.
Hang in there...it gets better!
Here's a link to my recovery journal during the first 19 days. While every recovery is unique, it'll show another person's post-Nissen experience: https://www.healingwell.com/community/default.aspx?f=45&m=2183443
Of course, if you're ever really concerned about your pain, or worried there might be something wrong give your surgeon's office a call. That's what they get paid the big bucks for! I remember calling mine more than once...