You know it hurts! and it's probably not good to pinch, poke, or impede circulation in your Lymphatic System; aka 'your glands'.
Improper fit, worn out elastic, and those rogue wires that pop through their seams! all may cause a wire to poke you in your tender and sensitive underarm area.
Besides being excruciatingly painful, this is the area containing the glands that clean your Lymphatic System, your Immune System; your disease fighter!
A clogged Lymph duct is no joke! You don't want to disrupt the flow of the fluids that clean out virus' and microbes from your body. Your Lymphatic System is your Immune System, and despite the little information we get about that, it is! and a medical book will confirm it.
If a bra is causing you pain and discomfort, pinching and poking you, quit wearing it! Immediately! Search for a better fit, a quality product; and maybe opt for a different style. A sports bra possibly; no wires!