Caleb was the worst day sleeper. I had him in and out of the car 3 days a week for kinder pick up and drop offs (both older brothers did kinder last year) so the poor thing had no daytime routine and he didn't sleep through the night till he was about 14 weeks.

He was a cat napper and 2 hourly breastfeeder and it was bloody hard. I would come home, wack on a DVD for the brother who was home and just go to bed with him so I could at least get some shut eye myself.
If he wouldn't sleep then I would have him in the HAB or in the rocker chair. He spent a lot of time in that rocker chair watching me do stuff.

If sleep school or learning settling techniques appeals you then give it a go. I didn't try that but I know a few that did with varying success. Be preared for it not to be the answer to your problems. My SIL was in tears because it didn't help her bub at all.