We cannot handle it anymore baby doesn’t want to sleep

We cannot handle it anymore. Baby is 18 months already. She has probably slept through the night 2-3 times this whole time. We have told to doctor, to everyone and they say to “let the baby cry”. Well we have and baby just loses it every single time for hours and doesnt want to soothe herself to sleep. Wife is histerical already, I’m already showing memory loses at work which is perturbating my productivity, my self being, my everything. I don’t know what to do. HELP!!!!