Nice person?

I'm so tired to be a nice person!  Everyone is expecting me to do this, do that......

So I start to learn to refuse others, to be more fierce to others (esp. when someone cut the lines when I'm buying things).  My Mom asked me to have dinner with the relatives in HK on this Sunday, I said I can't, cos the last ferry to Shekou is 7pm from Kowloon, or 9pm from HK island, so I said I can't go, plus my E needs to go to work and Amelie needs to go to school on Monday.  So she said you can take the train via Louhu.  OMG, it takes an hour from Wanchai (the restaurant we'll have dinner), and then 40 mins from Louhu to Shekou.  I said the fastest and comfortable way is to take the ferry.  And Amelie needs to go to bed @9:30pm.  So I said I can have lunch with my Grandpa and Grandma, but I can't stay till the dinner time.  If the dinner is on Sat., it's OK, cos I can stay a night in HK.  But my Aunt has booked Sunday dinner for my Grandpa's birthday.  Of course, my Mom and my Aunt is unhappy.  But what can I do?  Amelie will be very bad-tempered if she can't go to bed, she 's not 3 yrs. old yet!  Why can't they think in my position? 

Yesterday, my Dad's wife called me again, and ask me to go to the lawyer's office with her during Oct. Golden week in Chine (a week holiday), and I said NO, I don't have time.  Then she asked for my Mom's tel., and I said NO, pls. don't disturb her.  Of course, she changed her side of story again, and I have no idea what kind of paper we need to sign, and so I asked her to send a lawyer official letter to my brother or else get a court order to persuade us to go to HK.

I'm that kind of person always saying YES to others.  Now I learn to say NO, and the feeling is not so bad!  Do you have a feeling of being tired to be nice to everyone?