Hi there...
reading your post was so close to reading my own words lately! I have been almost flippin bezerk with my own 18 month old - can I suggest, Pinky McKay does phone consultations if you like? I made an appt but it didn't work out but I'm still thinking about chasing her up although things seem to be HOPEFULLY settling down.
I have read a bit though about an 18 month sleep regression which seems to be very common. Although
DS has always been a crap sleeper but I'm not often tearing my hair out.
So I don't have too many useful suggestions except that this IS a phase and it WILL change and you're NOT doing anything wrong! The trick...is survival!
Hang in there xx