i have read in the past that it could be one of three things
diabetes / hemorrhoids / worms
if it is worse at night could be worms, common, just takes a few pills taken once (amount depends how much you weigh)
Try Hydrocortisone cream to prevent itching. Don't use too often though.
I had the same thing and it went on for months I was too afraid to go to the doc. All it was... is a type of itching he said like "jock itch" gave me this cream nystatin and triamcinolone acetonide cream usp.
it worked in a matter of 2 days! Go see the doc, its worth it!