Sorry no advice but just wanted to say I feel your pain. My eldest was usually sleeping through by about 7 months even after I stopped the dreamfeed around then.
dS2 however is now 9 months and still waking between 1 to 3 times (i don't do a dreamfeed, sometimes he wakes when I go to bed, sometimes he sleeps on til later). Some days I am just so shattered I could cry - and dealing with the eldest by mid afternoon, now that he rarely naps, can be draining.
But - I/DH have tried occasionally to settle the baby in the middle of the night instead of me feed him. Sometimes he will settle - but often just to wake 30 mins/an hour later. So I guess he may be hungry. Regardless, I find it less tiring just to get up and feed him, than to try settling. I cannot shhh/pat endlessly at 230am.
So no advice - just maybe each baby is so different,
maybe this one just needs it whereas the others didn't.
Any reason this one is still in your room? My youngest was in ours til he was almost 8 months as we didn't have a room for him and I didn't want him in with his brother. We moved though and now he's in his own room it is definitely easier as we don't wake him when we go to bed, nor if one of us pops to the loo etc, and he sometimes sleeps later now that DH doesn't wake him when he gets up for work, nor does his brother if he's up at stupid o clock bouncing around.
Good luck, lack of sleep is awful.