mild pain during sex

my pain isn't super severe but sometimes my abdomen area feels inflamed and crampy at the beginning of sex and it makes getting started really hard, like we will both get really turned on, he'll start to enter me and then suddenly I cramp up and have to breathe and he tells me to calm down and we wait for the pain to subside a little before continuing and it's really annoying, I don't know what's causing the pain. Apart from sex, I usually have a dull pain in my abdomen area, that sometimes flares up into a shooting or stabbing pain. My doctor thought I might have endometriosis and they ran an ultrasound and it came out normal, sooo... I'm not sure what the cause is, but I want to manage it better. I don't want pain to interfere with me and my partner's sex