Infant first injection but have lump on hip.

Totally understand the worry, when my son got his first jab, I panicked too because the lump felt so hard and just sat there for weeks! From what I've heard, it's actually quite common for a firm little nodule to form at the injection site as part of the baby's immune response, and it can take several weeks or even a couple of months to slowly go away on its own. Someone in my mum group mentioned that a nurse friend of theirs explained it's basically minor inflammation, sometimes a tiny pocket of fluid, and doesn't usually need any treatment as long as it stays within a reasonable size. That said, I won't pretend it's always straightforward, if you feel like it's genuinely growing rather than staying the same or shrinking, that's worth flagging rather than just waiting, because my honest feeling is that "might go off" isn't always reassuring enough when you're watching it daily. Do keep monitoring it and please loop back with your PD or a specialist if anything changes, because they can examine it properly and give you real peace of mind.