Mini fridge constatly freezes?

everytime i defrost it after about 2 or 3 weeks the whole back wall of the fridge is covered in frost and ice and anything that i set in the back i frozen to the wall and the freezer is full of ice again and it time to defrost again and also there is alot of water leaking from the freezer door onto the bottom of the fridge and water is just standing at the bottom i dont know what to do btw its one of those where the freezer is in the fridge just has a little door to the freezer