My 12 month old use to be a great sleeper until her turned 1!

From the moment my son turned 2 weeks old he basically slept through the night. He would only wake here and there for more milk.

He turned 12 months old end of October and since then we have been battling this terrible sleep! He fights naps and just lays there and cries. Same with bedtime, he will fight it and then knock out for a few hours and wake up and be extremely unsettled. This will go on for hours at night and he will just be restless all night long despite what we do.

Is this a sleep regression? What can I do? I know my poor baby is tired but I have no idea what to do. My other 2 never went through this.