My Baby Won't Sleep!

Hi I'm pretty new two this. Let me start by saying I already have a 5 year old, she was an amazing baby, slept through from 5 months, and even now a brass band wouldn't wake her. But then there's my son! He sleeps for 20 minutes here and there if that in the day and night time. What even is it? i have tried everything.  Massage, yoga, special creams, quiet time, milk, risk, feeding last, bath straight after, calpol, nurophen, warm milk, cold milk, even banana milk!, white  noise in the room, utter silence in the room. My son will not sleep! I am so drained. When we was first born he used to wake up twice I was happpy with that but now he wakes up every half an hour after 11 and I don't know what to do. Any  suggestions will be amazing! TIA