What is this agonizing pain

For the last two days a last night I have been experiencing the most excruciating pain in my abdomen and lower back, it's not a cramping pain, but in my stomach it is a moving consistent pain. Its not hunger because I'm eating fine, I doubt it will be my period as I have no signs of it starting. It feels like I've got pressure from my pubic area going into my stomach which feels like I have pressure pushing my stomach into my lower left back. Its not trapped wind because I'm farting fine. The only thing I've been suggested is either ectopic pregnancy or stress pains. Like 3/4 times I have sex my partner cums in me. It hurts to move and everything. I've never known pain like this. Also before anyone asks I had my appendix removed years ago so its not that. Its worrying my partner a lot. Another thing, it's not needing to use the toilet because if anything that made it worse. Now and then the pain seems to also occur in my chest and i have to lie down as I'm just in so much pain