15 month old won’t nap or sleep at night

Hey mamas! I need help. My daughter’s been a good sleeper until a month ago. She has been refusing to take her nap during the day. She will fight with everything in her. At night (7pm) she would sleep for 15 min and then wake up crying hysterically. We usually let her cry couple minutes and then go in to calm her down, put her down and leave the room. But it doesn’t seem to work. She would stay crying for hours! there’s times she would wake up at 3am or whatever time and won’t go back to sleep anymore. Until after 3-4 hours of trying to put her back to sleep. At first we thought it was teething but it’s been a month or so. We have tried oral gels, Tylenol, Motrin and nothing seems to get her to sleep. She has always been on a schedule, she would do wonderful. I really don’t know what’s going on lately... today she had a physical, and I mention this to her pediatrician, she just said I needed to sleep train her again. I honestly don’t think sleep training is her problem. I mean I could be wrong. I am starting today to retrain her. But if any of you mamas have any advice, I would truly appreciate it. I am so tired and stressed 😫