3 + tests, but -bloods & scan ?

Hi everyone, 
Fiancé 32 & myself now 30 have been together 9yrs been ttc 4 of & in this time have suffered 5 mc. 
The worst was our triplets lost @ 19wks 3days back in Nov '15.
Doctors have been brilliant saying it can take a few months to feel better. 
So Jan 4-8 period turned up & seemed normal, by feb I was starting to feel unwell, but put down to expecting period. 
5 feb comes & goes started getting a little bit of nausea & gassy ect. 
15 feb finally it had arrived nope just a very light pesky dribble. 
Saw our FS for one of my check ups & mentioned the current situation to her  she asked if I'd done a hpt not yet. 
She suggested we could possibly be again now, so goes ahead & does all her examination all fine. 
Bleeding ceased that night & I just assumed was abnormal period again, morning of 18th I started getting really annoying intamittent cramps. 
I've never had ovulation pain or cramps & gas, nausea Started to increase. 
Took a hpt on 25 feb showed very faint line next one taken morning of 27 + so we scheduled a doc app. 
Straight up ordered bloods & scans, scan showed nothing ? Bloods however whilst not + for hcg they have come back as gestational diabetes.
Doc is confused & writes up my blood test forms to clarify, I'm freaking out & so she runs another urine test. 
We wait 2mins & it's showing -, she hands me the test 2 show fiancé & sends me next door for bloods. 
I come out from having these bloods done & I know I shouldn't but I checked it & the test was a blazing 2 lines with test line darker than control. 
I got home & showed the fiancé the test & he is just wondering the same thing how is any of this possible. 
Has this happened to anyone else here who found out you actually where pregnant ? 
Please help 
Thanks