Sleeping

Hello December mommies- my little man is 8 wks old is combo of breast milk n formula fed. I am having trouble getting him to sleep longer then 4-5 hrs straight at night. Lately it's been 8/830pm bedtime, 1030/11 bottle(4oz tried 6 but he has hard time finishing), 230/3 nurse, 430/5 bottle and back to sleep til 7/8. Any advice for a first time mom? I go back to work at end of the month and would ideally like him sleeping 6hrs straight at least.