Hello, it seems to me that you may be injected too fast too much in the same location, so a pressured liquid reservoir is built. When you change one of the variables sufficiently it should be better. The liquid needs to have time to enter the tissue. There is a technique in which you hold the skin between your fingers in which you insert the needle. It may help when you take the needle out to hold the skin maybe a little bit longer together so the liquid has time to enter the tissue. But Most importantly please make always sure that the animals are in no discomfort while working with them.

Best wishes

Uwe Y. Schwarze

Uwe Yacine Schwarze Thank you for the suggestion