I have 4 pregnant with #5, it seems like every time I hit the 30wk mark I'm stuck in the spoon position. It's the only way to support the belly and reach O. I'm slender so the weight of the belly in any other position will bring on the pulling ligament pain. Is not the most preferred position but it works
If you haven't already tried, you could try reverse cowgirl. . That's what position I have to use.