Biting and angry

how can i stop my JRT to stop biting and getting angry so easily? My JRT is about 6 months old and every time i play with his head(petting) he would get so mad and start scratching and biting and growling at me. how can i stop that? and his penis also has a deep cut or something down there. its really red and pus comes out of it. what does that mean? my mom and the vet says it just means he is a boy but what does that really mean? thank you for taking the time to read and answering my question :)