Advice needed

Shazeha
Hi ladies 
I had a miscarriage with twins 2 years ago and have been trying ever since. There is no pain like trying every month and getting a negative and then trying to restore your faith and to try again. 
I started my period on 20th April, should've been due my period around the 18-19th May but I still haven't. I did a pregnancy test (used pound land one) yesterday because I just couldn't help it but was a negative. 
My periods are always regular and on time so I don't understand why I am late, can anyone advice?