What to do during lunch at school?

I'm a senior in high school and transferred from a catholic school where I was well liked and popular. So I transfer to public school and I made some friends just not as good of friends as my old ones. So this new school I go to my brother goes there he's a tenth grader and has alot of friends. So during lunch I just do homework in the library because I work alot during the week and also because idk I don't wanna eat in the lunch room it's just different at this school. My brother always asks me where I eat lunch and he knows I'm in the library during lunch so what do I say. He thinks I have nobfriends but I do he doesn't understand how hard it is to transfer high schools durin senior year I just don't fit in. There's only 30 days left so what do I tell my brother? What's so wrong with doing homework durin lunch? Why do people (my bro) even care?