For the next weekor so,brush your teeth with a sensitive teeth toothpaste,that should stop your teeth being so porous - at the moment they are susceptable to absorbing stains.
In terms of your gums, i would recommend swishing your mouth with Corsodyl,which promotes healing, but not until you have used the toothpaste a bit, as it can discolour your teeth if they are ultra-absorbent.
In the mean time, its yukky tasting , but swishing your mouth out with a saline solution -boiled warm water with a few spoons of tablesalt willhelp heal until you can use the corsodyl.