Pain inside my butt!!!?

I am a 16 yr old girl and i know this is disgusting but i dont know what to do. I feel like i have some kind of pimple or something in my butt on the side (like behind the butt cheek). It hurts when i sit down or when i sit on my butt the way you normally sit down. if i move my butt in a weird way it hurts a lot also. I asked my mom and she said she wasn't sure wat it was bc she'd have to look at it. but based on what i said she said it could be a hemorrhoid. so i looked it up online and i am still not sure what it could be. I have been constipated a lot lately, so thats why i think it might be a hemorrhoid. but ive been constipated before and this has never happend before. I woke up with it this morning and the pain is getting increasingly worse throughout the day. and thats why i think its a pimple but i dont know. also i have finals so i have been sitting down a lot. plz let me know what anybody thinks! much appreciated.