My son is almost 8 months old and has never really slept more then 3 hours at night, I have tried everything!?

My son sleep changes every week, some weeks he will sleep 3 hours at a time, sometimes 2 hours at a time, this past week he has been getting up every 30 mins. I have tried everything the doctor has told me and even most of the natural products like gripe water. I have tried co-sleeping, I have tried him in his bed, I have tried sitting up in the chair all night holding him, NOTHING works! His stomach is not hurting because I give him tummy soother at night. His teeth are not bothering because when they are I give him teething tablets and Motrin. I am desperate for sleep because the past few nights I have not slept over 2 hours and Im also a student. PLEASE HELP!!! Remember I have tried pretty much everything. Thanks (;