What Could Big, Bulgy, Numb Area In Buttocks Causing Pain While Sitting Be?

I have area on my bum around the size of an orange that’s constantly numb, it also feels as though there’s a bulge on my bum muscle in that area – as though its twisted or something and when a massage it its aches. I can’t sit too long on an office chair because it starts to ache and numbs more with an aching sensations. Any ideas?