Confused

So this month was my 4th round on Letrozole cd3-7. I monitored for ovulation with opk’s and seemed to have ovulated CD 17/18, had minor cramps on one side those two days as well. I had no symptoms until a few days before expected af when I began getting nauseated every morning, soft stool with terrible gas pains. I put it towards af being on her way but on the 7th, when af was due, I only had light spotting on some toilet paper late that night. So I put a pad on think this was the start, I had also took a pregnancy test that morning with a bfn. Next morning, only spotting on the toilet paper a bit heavier than previously, but still not enough to even make a drop on the pad. This has been going on for 4 days and had never happened before. I normally have a heavy flow on letrozole. Today’s is the fourth day and it’s basically gone minus some extremely pale pink spotting when I wipe. I also had brown tinged ewcm earlier today, and woke up extremely dizzy and with a terrible headache. I have not tested since the 7th and wondering if maybe this was implantation bleeding instead of af. Anyone have any advice or insight? Thanks everyone 💗💗