Why am I always being left out? My whole life i've always been the girl being left out of things.?

Everyone says im lovely and always say nice things about me. But they often forget to ask me out. Most of the time they do invite me. But often they're all planning stuff and I'm just not involved. Me and my friend were talking about it and shes being left out recently too. And we dont no what we are doing rong. Like tonight my friend is going round my former best friends house (we're not as close anymore) why am i not invited? I've always been left out of things.