Get your testosterone level checked. Same thing happened to me and mine was low. Refrain from sex for a while as your burning out your bodies production of nitric oxide causing your ED now. Raising your testoterone level should improve your erection and orgasm problems.
This is quite an abnormal case. Urologist can guide you or sexologist. Exercises like Male deer exercise, Sat kriya( yoga), Energy yoga locks, anal peripheral prostate massage or abdominal prostate massage can help to get orgasm. Google for the above techniques.
The only thing I know to tell you is go to the doc
These marathon sessions may be counterproductive as with anything that is repeated for such a long time without success. All this continued friction motion would tend to deaden the nerves on your skin I would think. Do you shave your shaft? This may seem minor, but anything done to the skin would affect nerve sensations. Have you tried just curtailing intercourse for a few days to see if there's any improvement?