13 weeks pregnant - am I crazy? πŸ˜”

Can anyone help me?
I posted before Christmas because I found out I was pregnant. I did about 15 pregnancy tests and they were defo positive. I posted a couple of pictures on here because they started off quite faint but after about a week they were solid positive.Β 
Anyway, I'm 13 weeks now (or I should be) and I've had spotting, cramps and vomiting so I went to the doctors tonight. She did a urine test and it was negative?! She said if I've definitely not passed any 'products of conception' then it means I was never pregnant because you can't get a negative pregnancy test if there's any pregnancy tissue in your womb. Has anyone ever had anything like this happen to them?Β 
She's basically saying because I've not had any heavy bleeding then I can't have had a miscarriage so that means I was never pregnant?Β 
Someone please explain what's going on, how can I not be pregnant? I don't want to have miscarried but I can't understand how I can never have been pregnant. I'm so upset and stressed. I'd appreciate anyone telling me their experiences. As far as I was aware until today I was happily 13 weeks pregnant πŸ˜”