Anal tension during intercourse?

Hey guys,

I've only been sexually active for a short time. And had only begun exploring my body not long before that; my problem is I experience anal tension during vaginal intercourse every single tme, I know orgasams can involve anal contractions' but I'm no where near one when this happens, its quite frustrating as it takes away the pleasure and theres no way to relive it, the feeling is very much like wanting to pass gas' but being unable,

My vagina is normally very tight' and so I doubt weak muscles there are the cause. None the less I still do cagels occasionally. Also I don't have any ailments or issues regarding my partner,

And so does anyone know why my body is doing this?? I've searched everywhere online but I've found nothing.

Thanks,