As the others have already said Battle Master Level 7+ (Which is no option for you atm)

Is your DM throwing random encounters at you which you simply can't beat?

1. You might want to discuss with him that throwing deadly random encounters at you is not what you want if you can't determine the enemies power level.
2. If your GM insists on keeping the encounters as they are maybe he can figure out a homebrew rule which assists you and is not overpowered.

I don't see any other options except the items listed by nwp.

As the others have already said Battle Master Level 7+ (Which is no option for you atm)

Is your GM throwing random encounters at you which you simply can't beat?

1. You might want to discuss with him that throwing deadly random encounters at you is not what you want if you can't determine the enemies power level.
2. If your GM insists on keeping the encounters as they are maybe he can figure out a homebrew rule which assists you and is not overpowered.

I don't see any other options except the items listed by nwp.