Why is my mmr so goddamn low?

Because being Bronze 4 or Bronze 2 does not matter with the LP gained. Being at the appropriate MMR for rank does.

People will say, get to promos. DODGE, DODGE again (skip a day if you want). This will help "boost" your MMR so eventually after a lot of winning you will get decent gains. You don't need to dodge only in Promos. You can also dodge normal ranked games, especially if the team is stacked against you. Promos are just a safer place to dodge because you absolutely won't derank (you never will off dodge alone).

First dodge of the day, -3 LP. Second dodge, --15 LP. You will lose LP even when you dodge promos.