Home life.. (Bit of a rant)

So to keep a long story short I have lived with my BF since I was 16 y/o, with his two parents and 3 siblings. And I am so extremely grateful for them to welcome me into their house, keep in mind I have paid board/rent since day 1. 
I was expected to contribute to the house hold chores, which I was happy to do so. I aways clean up after myself and then some. 
The mother has since moved out of the family home and the eldest. and I am now 20 years old studying, working and pretty stressed. I share a bedroom with my boyfriend, a bathroom with 2 others and the kitchen with everyone. 
The thing is I look after myself and my boyfriend, cook and clean up after ourselves and maintain our room ect. I still do all these house hold duties such as clean out the fridge, pantry, bathroom and toilet. I also clean up any mess that I see such a emptying/ loading dishwasher, taking out trash etc. BUT! No one else but the farther does anything!! The mother even asked if I could clean the bathroom downstairs which I do not use, so I disagreed. I feel like it is so unfair, the siblings are 16 and 18 and they can't even put there dirty dishes in the dishwasher after their dad has cooked them dinner. 
The parents excuse is that we wouldn't have wanted to do that at that age either, but we defiantly did our best, we even use to cook the whole 7 person family dinner several times a week.
While I'm not complaining about the amount I do as such it is that I am the only one expected to contribute..... Am I being a bloody sook or do you agree that the kids need to step up! I feel like a mum cleaning up after these teenagers!!