Janesville police are looking for a man and a woman after an armed robbery at a south side gas station and convenience store.  Police were called to 1002 South Jackson Street a little before 8:30 p.m. Saturday.  Officers say a man and woman entered the store and the man walked behind the counter and displayed a handgun to the clerk.  The suspect hit the clerk in the head with the handgun and stole cash.  The suspects are described as a heavy set black male, about 30-years-old, with short hair.  The woman is 20-25 years old, of mixed race, with orange colored hair bangs and two nose piercings.  The suspects may have fled the scene in a silver or gray small SUV.  The clerk was treated at the hospital and release,