Just joined, advice needed please!!!

Hi,I have just joined the dog forum as I really need some advice. I got a rescue dog over a year ago, he has taken along time to train and I have put all my efforts into it. He now understands lots of commands ( he completes these when he chooses to ) however he picks and chooses what he wants to do and when he wants to listen.
He has always had a bed on the hallway so as he can see us all night long, he is allowed in our room during the day but we have had to put a stair gate across at night. The main reason for this is because he was disturbing us during the night when he could wonder into our room and would not settle. We did this around 6 months ago.
As I stated he seems to listen when he wants to and looks away when I ask him to do something he has previously done with no issue. The last couple of months he has run under our bed when I ask him to go in his bed or when he sees us settle for the night and refuses to come out. I have now blocked under the bed as I do not want to ban him from our room completely, he just sits on my bed and when I ask him to go to his bed now he looks away and refuses to move. I have to pick him up and then he tries to jump out of my arms and pushes the items I have used to block the bed with!! I then have to wait for him to come out and try to get him into his bed again. Once he is in his bed he sleeps fantastic all night long.
I was extremely firm with him tonight as it's just getting too much it seems to go on forever at night, I think I need to block the bed with something better but I want to understand why he listens sometimes and other times doesn't. He gets lots of love,attention,walks,play time etc so I do not get it?! I am currently 36 weeks pregnant and the whole situation is making me so stressed because he won't follow basic commands.
My dog ended up shaking in his bed tonight as I was firm with him and now I've ended up crying because I feel guilty.
Could somebody please offer some advice???
Thank you
Lauren.