Im really sad lately...I feel like I should be more loving towards my family...?

Ok so I am a 13 year old girl (14 next month) and I just feel really different.Not really depressed or sad..maybe more mature or something? I'm not mean to my family,but for some reason I feel like I should be nicer to them.Every time I make a mistake my mom lectures me about how I am cold hearted and should tell her and the rest of my family I love them.She just got remarried a few months ago my real dad left before I was born.My step-dad is ok but he has 2 daughters and they are very rude and I really don't like them.The oldest is 25 and the youngest is 12.They hate me and my brother.My brother is 23 and he's cool.He's always been nice to me,but he's a dropout and so my moms disappointed in him.I have this problem..I can't tell my family that I love them..no matter how much I do..I don't know why and lately I feel like I should but for some reason I'm scared.I even want to hug them sometimes,but I don't..It doesn't bother me to hug my friends at school or tell them I love them..when they could never compare to my family.When all my mom does is say how cold hearted I am for not telling them.My brother and my other family members dont say much either.What is wrong with me???