Bedtime/nap time battle ground

So in the last week my little boy has been refusing naps I always offer them to him when I feel he looks tired ect I always ask do you want to try for a nap he says yeah and waits for me to take him up to bed. As soon as he gets up stairs and into bed he has a absolute break down chucks everything out the cot.. all his dummy’s everything even now he’s pulling the fitted sheet off. I go in put everything back together give him dummy’s and leave again reminding him it’s time for a little sleep when I am there he lays back down the second I leave it’s repeat.. over and over again I don’t say anything to him when I return the following times just put his dummy back in the bed not handing to him but just in the bed and leave. Then after a hour and 15 of trying I just get him up he’s absolutely full of life then at 5 he can bearly keep awake. He’s exhausted. But he always goes to sleep for 6:45pm and because he’s over tired it’s Carry’s on much much later and if he wakes up in the night like last night he woke up at 3am he’s still awake now and will not nap. Any suggestions on what could help it doesn’t appear to be teething. A regression maybe I am absolutely exhausted and heavily pregnant I just want to know if there’s anything I could be trying xx