Well then it looks like your going to find a new boyfriend
I agree. If you sneak around and try to get pregnant, in other words manipulate the situation, he will probably be permanently furious at you (and with good reason. A guy has the right to not want to have to support more than two kids, it is emotionally and financially draining.) Find a guy with no kids who is eager to have some.
Then I guess you'll have to find a new man who does want babies. I don't see any alternative, do you? You want babies, he doesn't cause he already has 2. Sounds like you're at an impasse.