insertion techniques painful?

[dubpistol]

hi
have any of you guys ever tried jacking off but with a dildo up your ass?
i have had this before with my GF but i was trying it out solo yesterday
while jacking off to some domme TS pics and fuck me it really hurt
i could hardly get it up there, anyone know how to relax more or what lube to
use, im always freaked that when i finally do get to make love to a TS and
they want to penetrate me I wont be able to recieve or elsse it will hurt like
hell. its the same when my GF does it to me.
whats a boy to do?