Why do i get red lines on stomach after injecting insulin?

People please help my doctors say its nothing to worry about, as long as it doesn't itch and don't get any hives, which I don't. But I'm wondering why I get them, they do fade away after a few seconds. I use bd nano needles, the smallest ones they have. I'm wondering if its just from multiple injections a day idk tho if anyone knows of anything let me know!! Also sometimes there are red looking rashes that appear for a few days then go away!! Thank u all