How much of that 100iu/45mg solution are you injecting at a time. That's a very concentrated solution to inject, I am betting that is going to be your issue. You could also inject the same amount of b water and see how it compares to the tirz solution injection.
For sure add 3ml of water next time. Try injecting in your stomach again, and also try your upper thigh to see if there is a difference. I would also inject the same volume of bacteriostatic water in both spots (opposite) to see if that creates an issue as well.
The last thing I will add that probably has nothing to do with it is how steady you are holding the needle once its inside you. I had a friend that was getting spots like yours, but then the times that I would inject him he wasn't. Seemed super weird, so I asked him to inject in front of me. It really took him like 10 seconds to push the needle all the way in, the another 45 seconds to inject .5ml, and shook pretty bad the entire time. Since the tips of these needles are razor blades, I am sure he was just micro cutting himself up every injection.
Once we try all of these variables we should be able to help you out quite a bit or at least deduce that your Tirz is bad, or for whatever reason doesn't agree with you body.