What Causes Brown Blood Discharge With Cramping And Nausea?

Hello! I hope you can help me with an answer. I am a 42 y.o. mother of 3 with the youngest being 7. I have had 2 miscarriages since then in the last 3 years. I am usually really good at knowing when I ovulate because I get severe cramps and mood swings. My periods have been very irregular. But I started my last one on January 17th actually a day early. It lasted about 4 das which is the usual. The day after it ended I started getting really bad cramps accompanied by a major mood swing. Just as if I were ovulating. I had unprotected sex on th 22nd and 23rd. Now today a little over a week I discovered brownish blood in my vagina along wih slight cramping and some nausea. How possible I that I ovulated really early in my cycle, which I have suspected in the past and this is actually implantation bleeding? I have been researching on the internet so now I am really freaked out andstressd. Please any info or advice yo can give would be so helpful. Thank you!!!