Possible miscarriage?

I am a smoker and suddenly around the time of AF they just started to make me feel nauseated, AF was 3 days late, I had one really bad cramp I had to breath threw and keep myself together, then I started to have spotting. For me, I dot spot, AF always hits hard and fast. I had more cramps but I normally cramp pretty badly, the next day was like normal, heavy AF but with quite a few clots. It didn't really last much longer than normal, but it did end with a darker almost brown colour. Which again, I never have. I'm not sure if it was a pregnancy I was unaware of or just AF was different that month. Anyone have any ideas? Thank you kindly.