How do I try to be happy?

Here's a little background information: My dad was diagnosed with Stage IV Spindle Cell Sarcoma in May of 2010, and fought cancer until he passed away on August 21, 2013. I wasn't even 13 before he died, and we were very close. My dad was my best friend and hero, so it has weighed really heavily on me. My mom has already remarried and we moved in with my step-family. I can't stand living here. I hate every single one of my step siblings, but I know I shouldn't. I don't even know why I hate them. Anyways, I have a lot of friends where we used to live, about a half an hour drive away. My mom gets really frustrated with me whenever I ask to visit. It's not that I don't have a place to stay, because I have relatives who live there. She says I need to stop living in the past and make friends here. She thinks I don't try, but I am a very shy kid and she barely spends any time with me, so I can't tell her otherwise. In all truth, I have tried too hard. I have held in every emotion I felt since my dad was diagnosed because I didn't want to cause a problem. That's three and a half years. This is the first time I have asked for any help. I have tried to make friends, only to be rejected. I just want one real friend who would always have my back, just like my dad. I hate every second I have to breathe. I want to be happy, but I honestly cannot see how. Please help! Any and all suggestions are welcome.