Sex penetration hurt really bad can barly sit up almost phetal position. Not pregnant. What could b wrong?

There's just no way to even guess online. This is something that must be examined in person. There must be a pre-existing condition for ordinary sex to bring on this much pain. Hopefully it's more a matter of hitting a major nerve that was already pinched in some way (such as from weak muscles causing organ collapse) than a disease, but it could be anything.