I had sex yesterday and today I'm having a sore stomach and back. He didn't cum inside

Firstly, it is too early for your stomach / back pain to be related pregnancy.
As to whether your sexual intercourse session will result in pregnancy depends on:
- Where you are in your menstrual cycle? (IE are you close to ovulation)
- Did your bf unknowingly release a small amount of semen into you, even if he didn't completely ejaculate?

I’m not sure where I am at in my menstruated cycle and no he did not at all. He did not release any semen af all.