I had spottings between 11-13 weeks too. I was told it is pretty common and as long as just spotting is ok. But I wasn't able to see my OB in the same week as he was away, I went an emergency and had ultrasound. It was so relief for me to see the baby movement and heard baby's heartbeat. It was not fun waiting for 6-7 hours in the hospital but it was peace of mind for me as I had 3 miscarriages before. The doctors couldn't identify the cause but it stopped after 13 weeks. If you still continue spotting and increasing amont or color changed to more red, you should see your doctor. Hope you are doing better...
You should call your midwife. I had spotting when i was only 11 weeks pregnant but it was only little dots and had turned brown after. I did go and get checked by the early pregnancy unit and baby was fine. I'm16 weeks now