18 month old sleeping issues

[chocolatedrops31]

My 18 month old who has never been a great sleeper but has had long bouts of sleeping through, generally after sleep training, has for the past 3-4 weeks been waking almost every night anytime from 2 am onwards and not going to sleep for another 1.5 hours. I was offering water/medicine and as a last resort milk, but think she grew dependant so for the last 4 nights have left her (after 1 check). She goes from crying to chatting to long periods of silence to crying to chatting again, but each night it takes over an hour for her to fall back to sleep. If I go in, she throws a toddler like tantrum because I'm not picking her up. At a loss because leaving her hasn't solved anything (except on night 3 when she slept through but woke up tired and grumpy at 6:15).
Her normal nap time is 1:30-3, but today I pushed it to 1:45 in case she's under tired. Not sleeping 12 hours does affect her..she's tired and grumpy all morning.
She now goes mad every time I put her in her cot..whole thing is making us both miserable..any tips please?!