I desperately need some help!!!!!

I have a patient that is in heparin and also insulin dependent. Her abdomen (heparin and insulin injections mostly given at this site) is becoming bruised and nodules are felt in some areas. How can I give her the heparin injection without causing this "trauma" effect? What is it that I am doing wrong when injecting the heparin? Can someone please assist me in this issue. As a new nurse, encountering this problem its getting me scared. Thanks for your help.

Sincerely,
Fonzy from South Jersey