Anyone had a bfn at 10 days late and eventually a bfp ???? ?

Hi there I'm hoping for some urance !! I was due on on the 1st December I have been trying to get pregnant for 4 months and all I keep getting is bfn's I've done 4 superdrug tests so far I'm getting so fraustrated I have a little boy already and tested positive a couple of days late but not this long !!! Do doctors in the uk do blood tests if asked ?