An 18 month old should be sleeping through the night, nursing or not nursing. He should have been doing that for a very long time. Are you saying that he is not (either never was or not now) and that's why you're not getting sleep? Or is he insisting on sleeping in your bed now, to be close, when he did not before?
Hard to answer without knowing the specifics. But stopping nursing and being cranky can be due to other things. Ears? Teeth? Fever? Are you sad about the weaning and maybe he is picking up on your emotions?
If you rule out medical issues going on, then I'd say he you need to ride it out - that means taking him back to his crib/room at night. It also means someone else taking care of him - dad, grandma, great grandma, uncle, whomever. You cannot become the only person who soothes him or puts him to bed. If that has been your pattern (which some nursing moms do), then that's a mistake that needs to be rectified. You should not be the only one not sleeping. Get an air filter or white noise machine, anything to drown him out, and have someone else put him to bed in the middle of the night. Go out (by yourself, if necessary) during the early evening and have someone else put him to bed at his regular bedtime. Have dad take him out in the car at 3 a.m. until he falls asleep if it's the only way for you to get some uninterrupted sleep because you can hear him over the air filter/white noise thing. Do not be the only one who is in charge of caring for him when he's fussy.