Two years ttc

Hi I’ve been ttc for almost two years now with my fiancé, I have had blood tests done and they’ve all come back normal. I have an underactive thyroid but my levels are apparently normal. Just so confused as to why I haven’t fallen pregnant yet. What’s the next step to take? I lost my son after birth in 2017 followed by a miscarriage a year later so I’m feeling very disheartened and worried I won’t fall pregnant again 😔