I feel like the 5th wheel

So ever since May when my now ex boyfriend and I started going out, my friends have been treating me differently.. if I want to do something I have to call them or else they never call me, ok I will admit that while Ethan and I were going out I did center my attention around him.. but I'm a 16 year old girl and he was my first real boyfriend. Well here's the deal now that we're broken up I try to hang out with them all the time although they never call me or anything.. they don't seem to care about anything I pretty much feel like ane extra wheel. My friend and her boyfriend were that way too and I still called her but no they never bothered because they always assumed I was with Ethan. Well here's the thing that really makes me mad... they all went shopping today for homecoming dresses and none of them invited me, I felt so left out I mean sure I do have my homecoming dress and everything but still they could of been polite and asked me because the know I would have asked them all.
Grrr I don't get this and don't know what to do...