Hi I would really not recommend the fleet enema as it barely gets rid of anything. Mineral oil is not a good substance to put into your body. If you go to the drugstore walgreens etc they always have an enema bag that you yourself fill up with water, olive oil, coffee, etc. This allows you to be fully aware of what is in it rather than pre chosen liquid. Also with the fleet enema there is so little water that goes in. If you use your own enema bag it will hold about a quart of water. I personally will do about five bags or until the water runs clear.
Probably the pain is your body reacting to the mineral oil, the contents of your colon or large intestine shifting, possible gas pocket, or something of the like. Do another enema to clear out anything that is in there. Do you get constipated? if you have any more questions that I did not cover I would be happy to share more enema tips!