As Lyme Lyte said, many new moves are painful. However, as Chem said, inverted crucifix is basis from invert to other things. Of all the things I learned, inverted crucifix was one that "did not" hurt, wonder if your vitamin deficiency causes your pain. Many of us get black/blue when learning things where skin is taught, grabbing, etc. so don't know if it's deficiency related for you or just part of poling.
As you said, ignoring the pain can allow you to get into position. Even though some things are more painful than others, getting passed the pain is the same for many moves. I remember learning Superman, OMG, soooooo painful. Now it's sooooooo fun to do.
Just "hang in there" and it'll get better. Keep us posted.