What Causes Dark Red Bleeding During The Sixth Month Of Pregnancy?

Im 6 weeks 2 days pregnant and since 11.30 this morning ive had dark brown period type bleeding and light period type pains with a slight back ache, this is my second pregnancy, first one was delivered 2 and a half years ago by c section. i am just wondering if this could be a miscarriage? The bleeding isnt too heavy but enough to make me worry, it is just like a period only the blood is darker than my normal period. any advice appreciated, thanks