Lyumjev is known for stinging/painful injection sites/entry unfortunately. It’s just one of the drawbacks of the quicker acting insulin’s.
Not everyone gets it as a side effect but some people will feel stinging when the insulin goes in and/or sore sites. I sometimes feel stinging when it goes in but it always makes my pump sites sore/red.
It’s one of those things that you either put up with it because you like the quicker acting aspect of it or you go back to Novorapid. Personally I just put up with it.