everything starts to hurt??

whether my man is going down, using his fingers, his tongue, I'm using my own fingers (I kinda only do clit stuff, my nails are too long for anything else), once things start feeling really good they quickly start feeling really bad. my legs get super tense to the point that it hurts, sometimes I also get this feeling like I have to pee, but the leg tension makes me want to stop everything. I stop, I'll tell him to stop - I don't want to stop, but it hurts! does the pain subside eventually? quickly? is this natural? is there a way to avoid pain in your legs? does this feeling mean I'm about to orgasm? I never have before and EVERY time somethings going on down there, this happens, so I like to guess that's what's going on but I have no clue??