Hi I take carbamazepine 400mg twice a day. I got my period 4 days in advance for only 2 days (I usually get my period for 5-7 days). After some reading, I thought this might be decidual bleeding (and not implantation bleeding)as the flow was similar to a period. I have been having early pregnancy symptoms such as mild lower abdomen cramping, mild back pain and feeling nauseous. I took a pregnancy test based on hcg this morning and I was surprised (and disappointed) it was negative. Could this be a false negative result due to my medication although I am on low dose? I am also confused because of the two-day period I got.