Help need some advice

My bf of 13 years and I have a son together that is 7 yrs old. I want another one before it extremely to late for the both of us. Since we're in our early 40's. The only problem is that he doesn't want to move, all he wants to do is lay down and for me to get on top. That's great and all but the only problem is that I'm a plus size girl. So the of way we have had sex was reverse cowgirl and doggy, in between that. I can't explain how. So we when start off we're good but then it I get tired he pulls out and starts playing with himself, when he's ready he goes to put back in but then all of often he can't find the hole and it's because he doesn't move. And he loses concentration and doesn't do nothing no more. So my question is when am I going to have my second child. Mine guess is NEVER. Any advice