Why do i feel like a outcast?

lately i have been feeling like a outcast. because when i hang with my friends a,b,c they all seem to treat me like a outcast in some type of way and these are my main friends. friend a im the closest to he treats me like im his brother. but i think me and him have leadership issues sometimes like whos goin to start a conversation first. but we do alot together and we trust each other with secrets.but when he is having fun with other people it seems like he forgets about me and i feel left out (alot of people like to be around him) . friend b is cool but it seems like sometimes hes not cool with me like one time were eating and me and friend c were sitting together and he asked fried c to sit with him and didnt ask me but friend c did which made me wonder about hm and kinda made me mad but he still does alot of stuff with me and gives me rides when i need then (hes the only one in the group with a car). friend c i wonder about hard because hes cool but we can never hold a conversation and he usaully leaves me for friend a or c. sometimes tries to invite me in to situations with the group but we never really talk that much and im always the last person to know something from him. when friends A,B,C get together its like i dont exist in a way and they do more stuff together without me and never call me or text me 2 join them.but one situation was when i was playing basketball at a open gym and they were all saying stuff to each other and nothing to me and it was lke they forgot about me.another time when we were goin on a trip and they were igning room mates they had a choice between me and so guy (i wasnt there i was sick) and friend A told me he didnt say a word to defend me or he wasnt paying attention and they chose the random guy. in a way everybody seems to be brought together by friend A idk y but friend b always brinds up stuff they did together and friend C always seems like hes trying to find a way to be around him.another example way when we were suppose to go lifting and friend a came to get friend b and always seems to notice him first. in away i feel like im slowly being replaced. also i feel like a outcast because i was walking in the hallway with friend b and its like every person that came by said hi to him or he said hi to them and that made me feel like a outcast and lame but he always seems to leave to go do something else when its just me and him. this about me im kinda quiet around certain people im loud im shy and not that funny but have my days and i dont kno how to start a conversation or keep it goin (Unless its with friend AorB) also im clumsy. but i think the main problem is that im so quiet and alot of people dont notice me also i have a problem with talking to girls. what can i do to not be a out cast and kno how to start a conversation and keep it goin and get more noticed and have more people hang around me