Fasting and gas

hi, i am 40 days into a fast and was fine all along .but about 2 days ago i started getting gas .so bad that i have ab. cramps at times. i have been drinking water with lemon each day and juicing .i have had juice each day of mostly greens cabbage,celery,cukes,kale,parsley and add some garlic and lemon and beet. ive been fine all along till a few days ago ? is this a detox effect or something else?
ive never had this on a fast before.