I have an aggressive lhasa apso, what should i do?

My lhasa apso is about 5 years old and he is aggressive for no reason. He bit my baby cousin bc she tried to pet him, you think that's right?.. then when i need to shower him and cut his hair, he bites me... he has never been mistreated or anything. He doesn't let anyone around him.. like he someone tries to pet him he jumps at you and bites. I really don't know what to do? do i need to take him out more since i barely have time to do so.. my siblings work and stuff .. & no i don't have the time nor the money for professional help. please help.. and oh he is very healthy, got him checked last week at the vet