I'm really scared and confused

So my boyfriend and I have never had sex without a condom we've never had any accidents. We are extremely careful. That being said, sometimes he will put it in without a condom just for a couple seconds and then takes it right out. We just like how it how it feels! But whenever he does he always checks to make sure there's no pre-cum. Again we are very safe! But anyways he did this about a week ago. And now for the past three days my boobs have been hurting, and I've gotten cramps a little bit off and on, but my period doesn't come for another two weeks. That's why I'm feeling very confused. I am in my fertile window right now and we haven't had sex since I've been in it. I'm just freaking out. I do not want to be pregnant but how would it even be possible? Even if there was Pre-cum it's very unlikely to get pregnant from that. Is it possibly from stressing? Idk I need encouraging words. I'm 19 and my boyfriend is 18 not wanting babies.