itchy buttcrack

Lol it sounds horrible and feels equally as horrible but my crack is so itchy starting from the very top of it all the way down to right before my anus. I don't really know what this is and why it's happening do you think it's a yeast infection or somehting? it gets so itchy that it keeps me up for a half hour just scratching it over my underwear. I've been changing my underwear at least 5 times a day because of how much I scratch. sometimes it's so unbearable that I have to just get in there and scratch it bare but skin starts to come off I disinfect my hands after I do it because I'm afraid it's some kind of disease. maybe it has to do with being pregnant? I had to use some of my Sons diaper cream just to soothe it and I'm too embarrassed to tell my husband lol I'm so at a loss. please help me.