Why do I feel like I have to pee during sex?

okay, so I’ve never been able to orgasm with my boyfriend or allow myself to. it’s always been my vibrator and I; however, when we do have sex I always have an insane urge to pee. is this me on my way to climaxing or do I just have to pee? when masturbating I typically only focus on the clitoris so it’s a sensation I only feel with my boyfriend. any advice would be greatly appreciated.