Hi,
It sounds to me that you may well be hitting the 18 Sleep Regression. It's a challenging time to say the least, whereby all that you had in place re: sleep seems to go out of re window. You have my every sympathy - we had a tough old time here. My best advice to you in consistency, consistency, consistency. Stick to your routine as best you can. You may find that you need to do some earlier and longer naps and EBT to avoid getting in to an OT mess. Do your best to avoid falling in to any major AP traps. Think of it this way, just think how confused you are as to what is going on, how do you think your 18m is feeling? If you can offer your LO consistency through this horrible time, you will offer her reassurance and security - it's all as it should be and then when it's over you it will be easier to be able to get back on track without having too much to fix iykwim?
Below is a link to a support thread for parents going through the same thing which might be of some help to you, even if it's just up share your frustration!!!
18 month sleep regression support thread - Part 2Hena x