A.H.
Assuming you have ruled out medical issues I have two bits of advice: (1) It is so easy to get hung up in a routine and not notice that our children's sleep needs have changed. Around age 1 many kids drop a nap, so maybe he is getting too much sleep in the day. Spend a couple days watching him like a hawk for signs that he is getting tired instead of going on autopilot. Maybe it is time to drop to one nap. (2) If that does not work, cut yourself some slack and do what you need to to survive this time. Being overtired and snappy will just make things worse.
My son was like this from 5 1/2 months until age 2! Prior to 5 1/2 months he was a champion sleeper!
In desperation I read many, many sleep expert's theories and I have yet to find any practical advice on how to apply the cio method with a truly stubborn bebe! There is definitely something to be said for the circadian clock theory, but how to keep a child who can scream for entire nights on end and cry his way through nap time day after day on any schedule is a mystery to me! Each time we stuck to our guns with cio, we wound up exhausted and it took weeks to repair the damage and get him back on schedule.
What I ended up doing right or wrong was: to do whatever it took to get him down for naps then I insisted he start the night out in his crib but allowed him to come into bed with me during the night. At 18 months I stopped letting him nurse but let him cuddle with me. I wasn't 100% happy with this, but at least everyone was getting enough sleep to function. For a long time we had to put a hand over his chest to keep him laying down but eventually I was able to sit in a chair next to the crib, then move the chair further and away from it. Around that time he stopped calling for me in the night and now that he does not nap anymore we can leave him awake at night and have him not call for us until morning. Alas, some children just can't be forced to sleep through the night until they are ready.