Please help im sure im pregnant.

Hello I am new to this site but I love it already everyone seems so helpful. I have had my marina coil for 3.5 years and around 8 weeks ago I had awful pains (i think my coil slipped down) I've had nothing but trouble with it it took 3 years for my periods so even cut down from 10days to 2. Anyway so I told the doctor and I should be getting a scan end of Jan 2016 I told her I think I'm pregnant at the time it was to early to test. I've done 2 hpt both negative I would now be acording to my apps 5w 2d and I missed my last period but had 2 days of spotting just befre and I have experienced some pink discharge in my pants tonight but not much. I'm sure I'm pregnant but how can I know for sure xx