Butt Hurts

Tiffany
So I've been exercising, mostly running, lately and my bottom really hurts and feels strained. Does running strain your butt or is it another exercise I'm doing that I can't remember? 
Anything other than squats that build a big tooshy? 
Also I'm applying for the defence force and can't do a push up, I need to do 6 to get in, any exercises that can build up my strength? 
And I need a 6.1 on the beep test and can only get about a 4.5 anything to build that up? 
Thank you for any advice, anything would be great xx