why will he not sleep!

i really need some help girls as im getting to my wits end! Alex just will not sleep, he is awake till gone 12 every night and then is up after an hr if im lucky and atm he just will not go bk to sleep! he only has 1 or 2 30min naps in the day and thats take me over an hr to get him to go to sleep. i just dont understand why he will not sleep ppl keep telling me its my falt cos i have sleeping probs which makes me feel like crap! atm to get him to sleep i ave to let him scream for 20mins then feed him then he will go down. lastnight he was up from 5 till 8.30. he is such a happy baby he just will not sleep, i keep being told to stop BF and put him on the bottle but he will not take a bottle and i dont really want to stop feeding him.
i just really dont know what to do i cant just leave him crying. please help xxx