I know you said you've already done the whole drug thing, but do you stagger them? Tylenol every 4 hours, ibuprofen every 6. We do that, and teething tablets, and still at least once a week, he'll go down fine, and then wake up shrieking...I think it's the whole separation anxiety thing. We go in and hug him and give him his tablets or medicine, and hug him, he lays right down, whimpering, and when it seems safe to leave, we do so...and he shrieks again.
Sound familiar at all? I think it's just something that they all go through, from what my friends tell me.
Hopefully this will pass soon, and you can get some sleep! I know you're already tired from the pregnancy, so that's gotta be frustrating.
Hang in there.