I'm not expert on IV use. But something you may want to keep in mind. Pain down the left arm can be indicative of strain on the heart. Meth is pretty taxing on the heart. In the past when I've been playing with uppers+downers or multiple downers at the same time combined with too much caffeine I've sometimes gotten that flash of pain down the inside of my left arm. Even when totally sober if I've been pushing myself to hard and not taking care of my body I've gotten flashes of pain down that arm. I also once stupidly took to much loperamide and got heart palpitations combined with pain down the left arm.
It might not be a case of simply missing or improper injection. It could simply be your heart giving you fair warning that you're putting to much strain on it by mainlining meth to often.
I know once you cross into IV use that it's hard to go back. But it's doable and I've seen at least once person kick it over the years while still maintaining a heavy habit through other routes (mainly, snorting, smoking and rectal). Ironically, they'd done way too much damage to organs by the time they stopped playing with the needle and died within a couple of years from heavy alcohol abuse combined with what I suspect is damage done by mainlining research chemicals, opioids, cocaine and meth for so many years. But they did manage to quit the needle and they took a lot of pride in that. They were certainly able to control their use much more afterwards and while they carried the scars from heavy IV use for the rest of their life their health did massively improve for about 6-8 months until their liver finally gave up the ghost.