I have done my fair share of gear. Probably on the low side of this board. But you can tell when it is infected. I have had dozens of incidents like you have described but nothing my body couldn't handle. Except for last year. It was prop, 100mg EOD. By 48 hours something felt off. I didn't listen to my gut and did another inject. Day 4, I couldn't raise my arm. Felt like it was pumped. I took a 5ml syringe with 21g needle and aspirated my shoulder. About an inch deep into my delt is where I hit the abscess. Talk about being in tune with your body at that point. Because it sounded like a geyser when I saw that syringe fill up with puss.
Point being, it felt nothing like the dozens of other times when I had lump and it was red. It was a different beast.