I just took my weekly subq shot. The needle really hurt this time, and now there's a firm pink lump under the skin where the liquid is hanging out.

I'm not freaked out by this. I've done this 59 times now, and I have this reaction maybe 20% of the time. Of those times, about half it goes sway by the next day and half it stays an uncomfortable lump for a few days. Sometimes the needle makes me grunt in pain, other times I barely feel it. Sometimes the site itches almost the whole week. Luckily, sometimes nothing happens and I forget where the site even was. I rotate areas of the body where I inject (I keep a list of the sites to make sure I rotate) and there's no correlation between site and reaction.

My question is, does anyone know why it would be so different every time? I know people can have very different reactions, but is it normal for one person to pretty much have all the different reactions seemingly at random?