Unprotected for no reason

Just recently my so and I stopped using condoms. I'm not on birth control. I don't know why we stopped, I let him do it once without a condom because we've used them for a year and the sex was off so we wanted to try something different. Anyways, he pulls out before he finishes. I know there's pre cum and I know I can still get pregnant. I am in denial about it though. How likely is it? And how long after my period (if I were to be late when the time comes) should I take a pregnancy test
And on a side note, is heart burn and acid reflux a symptom of early pregnancy? Because this happened only after unprotected sex and I'm confused