Try mixing in some lido/epi or sodium bicarbonate 8.4 percent to bring the pH up near 7.5-8. That should cut the discomfort. Plenty of threads here cover the same approach if you search.
I did my first shot of GHK Cu last night at 23:00. It was 2 mg in 12 units after adding extra BAC water to cut the sting. Everything was at room temp and I injected slowly into the stomach fat. No burn or sting at all. Slept fine and woke up with zero bruising or swelling, but there is a noticeable dull soreness about the size of my hand. One write-up mentioned it could be normal inflammation from the copper. I am icing it now and wondering if a different spot, smaller dose, or massage would help. Any experienced input would be great.