Full time job/breastfeeding

FTM , I return to work in Jan and I have an 8-5 job, my boyfriend will be home with the baby, I'm concerned about not being able to pump enough for the first day or two, when I'm gone . Because I leave about hr/hr and a half commute... My son eats every 3-4 hrs with me , but others always assume when he cries he's hungry and I'm Afraid of him either being over fed and spitting up , and starved to follow ... Any suggestions?