Why did you head straight to FET? Usually docs will let you try fresh transfers first before frozen.
A few general things to look out for when doing FET: Embryo (I am a firm believer of blastos) and lining (Please make sure lining is clear from hydrosalphinx fluid, growths etc and at least 8mm. Ideal would be 10-12mm, nothing too thin, nothing too thick). Can work on the lining by drinking soya bean milk, red bean soup and food high in protein.
First cycle I did a fresh transfer of blastocyst without removing my hydrosalpinx. So doc believed that's the cause of that failed cycle. Subsequently I did a fet after removing the hydrosalpinx but still bfn.
I then did a 2nd fresh at another clinic and that clinic only does FET. Bfn too.
I did my 3rd fresh recently back at kkh and with a totally different stim this time round.