Marie- I'm thinking it's likely IB. Super common to get it about the time AF is supposed to arrive. ANd if it's brown, not red then it's old blood which makes me think that's the most likely cause. I'm thinking if it were AF you'd be getting red spotting or orangish-red. Also, cramps in early pregnancy are SUPER normal. If you worry about every pinch or poke you will drive yourself nuts. If the cramps get super intense and you're bleeding enough to soak a spot in your underwear then you should worry. FX for you hun, but I really think you'll be fine.