Supposed to be early weeks pregnant and this is happening. WTF is going on .... Please read!

Got positive pregnancy tests this week around 4+ weeks. 5 weeks tomorrow!!! Friday late at night I saw brown old blood (discharge) in my underwear cramping on my left side. I panicked and phoned the hospital they told me to come straight into A&E. Got bloods took my HCG was at 18. Urine sample was negative but i drank lots before I got tested so i could of dialuted the urine. They checked my cervix everything was fine, cervix is closed and no discharge or blood. 2 days later today i went in again for more bloods got bloods took waited an hour and they told me my HCG was 45??. They said their may have been something their and its just came away with the brown discharge. They are not treating is as a mc or ep. They said they want the numbers to come down so my body can go back to normal and heal to get rid of what ever it was (dont know what they meant). They said because my HCG levels are low their is no pregancy or baby because at 4 weeks plus it has to be in the thousands. So i dont know whats happening. They think it could be retained products after nearly 9 months when i gave birth in feb. I got 3 D&C's but thats imposible because ive had normal periods and have been regular. My cycle is 30 days. Period was 8th October and ovulated 26th October. My period is late. Tuesday morning ive to go back for bloods and see what the HCG level is but they are not concerned at the moment and they have also booked in for an early pregnancy scan.

What's going on....... Im wondering if I could be less than 4/5 weeks. Maybe 2/3 weeks pregnant I don't know. I just hope their is a baby if not then I don't know why my period is late and their is HCG in my system with Positive PT. Brown discharge for 1 day and cramping on left side.