I'm not sure if that would be spotting or just like an early start to my period

Okay so my boyfriend and I had unprotected sex a few times earlier this month but he pulled out each time before he came. I know that the only way to tell is by a home pregnancy test but I'm worried and could use some advice. I'm worrying because my boyfriend thought that pre-*** could cause pregnancy but a friend of mine had told me earlier that it cannot. So we looked it up and found that pre-*** can get you pregnant but only if there is sperm in it from a previous ejaculation but that the chances of that causing pregnancy are about 1 for 10. My boyfriend was also worrying because I had told him that for about 2-3 days I was having dizzy spells and because I had a headache yesterday and those can be symptoms of pregnancy. We looked up the other symptoms and my breasts aren't tender, I'm not naseous, I don't have fatigue (I'm usually tired anyways and I have been staying up late lately), I haven't had morning sickness or lower backaches, I haven't been urinating more frequently, and I haven't had food cravings or aversions which are all symptoms of early pregnancy. I know that the biggest sign would be a missed period, my period is supposed to come on Tuesday but it usually is about 6 days late or so. Am I worrying for nothing? Would it be too early to take a pregnancy test? I've read that you can take a first response test 6 days before your missed period. I'm just worrying a lot about this and I want to know now, I'm very anxious. Can somebody please help guide me and give me some advice? Thank you in advance. I haven't gained any weight but I've actually lost weight, I believe from worrying so much because it's making it difficult for me to eat. I don't want to be pregnant it was a mistake and I regret it and I've certainly learned my lesson. I just really need some help I don't know who to talk to. My period is supposed to come tomorrow and I noticed a little bit of brown blood(?) in my underwear and I'm not sure if that would be spotting or just like an early start to my period. Please help me