Thoughts?

Trena
I use to have an extremely irregular period, but since I started taking prenatal vitamins, probably close to 2 years ago, it got super regular, if anything, I would occasionally start a day early.
But back in July I was a little over 2 weeks late for my period with NO signs of it coming at all, when I normally have extreme cramping for close to a week beforehand.
I was really constipated and was nauseous a bit more than usual, and when I took a test, it was negative. AF did end up coming after cycle day 16, I believe.
Ever since then I have been regular again, as far as starting on time, but I only have medium/heavy bleeding for a day or two, then light spotting for 4-5 days, then brown spotting for another 3-4 days.
It isn't TOO different than before, the first day would be medium/heavy, the second day would be extremely heavy, third day would be medium/light, then day four would be light/spotting, then off and on spotting for 3 days or so.
?!What are your thoughts on this?!
It's been a little over 4 months now and I can't stop thinking: "Oh my gosh, what if I end up being one of those girls that didn't know they were pregnant?!"
I know that's MORE than likely NOT the case, but I can't help but wonder a little bit.
I've been TTC for 3 years now.