As you know; sexual excitement is 90% psychological - physical stimulation is obviously important, but if your big head isn't cooperating your little head isn't going to get the joy. We men have a tendency to psych ourselves out and, for most men, trying to get hard or get off is the joy-killer - it's easiest if you can stop thinking and let your dick take over.
Not that that makes it much easier, but it is a good thing to keep in mind.
Are you watching porn that you really like? Could help, at least until you get used to coming in your ass.
I've really enjoyed inserting some fingers along with my cock and stroking the sensitive underside of the head - kind of like jerking myself off inside my hole.
Not easy, but once again; letting go of the intention to cum may be your best bet - once the pressure is off you can just relax and enjoy it, whatever happens.
Thanks for the picture - love to see more!
Al