According to Mosquito World, a female mosquito continues biting and sucking blood until her abdomen is full. She rests for two to three days, lays her eggs and returns to biting.
The New York Times explains that people often suffer multiple mosquito bites from a single mosquito due to a variety of factors. Certain blood types coagulate faster than others, forcing the mosquito to bite several times in order to reach her fill. Also, mosquitoes do not always strike blood with every bite. Just like a phlebotomist looking for a vein to draw blood from, a mosquito often has to pierce the skin more than once to get a drink.