Brown to Light Red discharge?

Hi. So I'm 18, I'm ttc and then I'm not. But I'm just wondering. I have had sex with my boyfriend of 8 months a couple times in the past about 2 months. But only 2 or 3 times a month. We use the pull out method. I know that can still have a slight pregnancy chance. Anyway, I've gotten my period so far this entire year, in May my period came 4 days late, then June it came also 4 days late, and now in July it came 3 days late. Which is abnormal for me to get them that late. I already had finished my period just this past Thursday the 24. I had sex on Friday the day after it finished. There was no discharged. But now on Saturday I had a tiny brown to light red discharged & same goes for today. Before you ask, we did have sex 1 & 2 weeks before my period even started. And now I'm starting to feel a bit nauseous after I eat, and I've been having light headaches as well. Is it ovulation or implantation? Or am I just having too much in my head.