I’d be interested to see what happens if you add in a couple sites, like delts for example. Could just be a coincidence that it’s only happening on one side.

Are you fairly new to injecting Test? (1)If it's just virgin muscle(new to injections), I'm sure it's fine and your tissue will adapt as you inject more over time. (2)If it's from a shitty no label cheap source it might just be dirty gear. (3) Pull your test from the vial with one needle and then switch to a fresh needle to do the injection making sure to swab the site with 70%+ Iso Alcohol.(4) When injecting glutes use a 1.5" needle, maybe you're not injecting deep enough. (5) Maybe your left glute is straight and your right glute is gay. That would definitely explain why it itches. If that's the case I would swab that right glute twice to be safe.

That sounds like the symptom of an allergy but it doesn’t make sense because it would happen every time, every inj site until change or tolerance. I wonder if there is particulate under the skin causing irritation?