Candida coming out will make your bum burn. I used to get that whenever I did enemas or colonics. Very uncomfortable indeed.
Threelac was not helpful to me. It seems an overpriced probiotic, as there are many cheaper ways to replenish your good flora. Try making your own fermented veggies or yogurt ( if you tolerate dairy ). I did several Bowel Cleanses over the years. They are really essential, but you MUST also re-establish your good flora as well. As far as cleansing goes, think Bowels, liver, kidneys, and lymph. Do some reasearch about cleansing and visit some of the other forums here :-).
Most people with candida overgorwth have found doctors useless and have even been chastised and made to feel like idiots when they sought help. Doctors are taught nothing about wholistic health in school.