What Causes Severe Pain In Pelvis And Tail Bone?

hi

since aving my son 6 months ago ive had really bad pain in my pelvis ad tail bone it is alot worse when im on my period. also when im on my period i find it really hard to go for a poo. the pain just gets 10 times worse and i give up it feels like my muscles are not working. ive always experienced pain during sex but this is also worse now. at different times in my cycle it can go from just uncomfortable 2 really bad pain. ive een very constipated no matter how much fruit i eat

thanks