I have pain under the abdomen for months and pain during defecation but also pain in the coccyx i have gone to urologists and pathologists. what can it be? i have not found anything. the pain is like knives when i bend down or lie down and it leaves?

This may be proctalgia. Sometimes it is associated with constipation. It is very painful, but benign and evanescent/

You went to the wrong specialists. You should see a proctologist or a gastro-entrologist. It could be something related to your Anus-rectum. But without an exam a diagnosis can not be made. In the meantime avoid constipation, use a stool softener and try hot baths for the pelvic area. Hope you feel better.