Why arent my friends including me?

Lately my friends havent been including me as much as the used to. All winter i was busy with my sports and stuff so i never really got to see them except for the occasional weekend and in school. But now that its summer they arent really asking me to hangout or anything. Its already been 2 weeks since weve been out of school and ive only hungout with them once. They are hanging with all my friends but I feel like they are never inviting me anywhere with them. For example, They are all going to a party tonight at my other friends house ( were not close friends though) and they didnt even ask me or tell me about it. Only 1 of my friends actually trys to make plans with me the rest of them I always have to ask them to hangout and what not. What should I do? Ive been friends with these girls since I was very little I cant just replace them. Should I give it time? Should I try harder? Im stuck and I feel like crap