Help , when should i?

Andrea • Have an angel above, stillborn on 02/26/14
I dont know when to do a pregnancy test! I had sex on the 20/04 my nipples are sore and standing out more than usual, i had a BFN on the 4/05 , but iguess its too early right? when should i test myself? 
​Had sex on cycle 8 and i am now on cycle 27 my period came on 13/04