I was having sex and the condom slipped off my partner and got lost in me, not sure if he ejaculated yet or not. I think he was about to? But another thing is I checked my cycle and the day this happened was right in the middle of me ovulating…now it has been a week and I have been feeling a little crampy with slight lower back pains, nauseous too but nothing major... what are the possibilities I can be pregnant?

It's possible. There is no way for us to know.

You will have to wait it out and see if you miss a period and then take a test.