Did you DTD? Perhaps it's just from that. It's normal in pregnancy to have some of the capillaries on the cervix break and therefore bleed a little (hence brown colour). This esp happens after sex etc.....If there is no cramping and it's only brown (not bright red) and light, I don't think it's anything to worry about. However if you are worried, call your GP or OB or the midwives at the local hospital....