I use my buttocks for long acting and my thighs, and it stings like aaaah! I have tried slowly injecting the plunger and quickly, nothing. And this is because I feel I have been changed to Abasaglar recently and the pens don't agree with me, never had an issue with Levemir, or NovoRapid, I assumed this was because of NovoNordisk being superior in engineering their pens, however, you're using Novolog which is Novo Nordisk too.
I think for me it is the new solution in the pen, it never used to sting and has put a tear in my eye thats how bad it has stung!