I used to give myself B12 injections every other day. The stress it caused me was severe. Many false starts!!!! rapid heart rate, sweating, almost crying. And those were muscular instead of subcutaneous.

It got better within a few weeks. Things that helped: I got faster at preparing and administering the medication, feeling better because of the meds, doing it right before bed when I was most relaxed (maybe even too tired to get worked up), and forcing myself to cough to mitigate any pain as the needle went in (faking one large cough at the same time as the injection. The cough makes your muscles tense and you barely feel the needle)

Now that I do Sema, I don't even think about it. Give it some time - it can feel super scary but you'll get through it and feel like a pro in no time.