Hi There. I'm A 21 Year Old Female. Last Night

Hi there. I'm a 21 year old female. Last night i felt a lump on my bum crack. It's right in the center, at the top of my crack but down a little bit. It's pretty much rock hard and hurts badly. It doesn't hurt as much standing up but so very painful when i sit down and what not. My mum had a look but can't see anything, no redness or anything around the area, just the hard lump. It's quite worrying and any help would be much appreciated. Thank you for taking the time to read.