Having trouble with Riven (playing her)

Just so you know i only play her for fun, i'm actually trying to get better at her because i love the new Dawnbringer Skin that's comming out and want to be good enough with her to win with and enjoy myself.

The issues i'm having is that i feel like i deal very little damage, even if i auto attack between each Q, perform the Fast Combo properly or trade properly, it just feels very weak to me. I take Fervor of battle most of the time (i don't know when to take Thunderlords instead) and still feel kind of weak.

Edit: i tend to build BC or Death's Dance first, i'm basing this off of what i see higher ELO riven's taking and the vast majority of riven's taking, it seems you don't build tiamat first anymore.