Air goes into the syringe every time. Am I full of air, is the air coming from outside due to the 23g needle, or is this normal? There is no air in the needle at the moment of injection, just when aspirating. It seems very strange.
Pulling back on the plunger creates a vacuum and what you have noticed is just dead air space due to the compression of the fluid, a a result of increase in pressure within the syringe. It is also likely that some air may have entered the syringe as well, don’t worry.
I thought you were full of shit. Just kidding man, it’s normal. No worries.