Why don't i fit in with anyone?

Here's the thing, i think im too nice, i am always trying to be nice to everyone helping them out and such, but it seems as if people only come to me for help with things or when they need me to do something for them, i think i have lots of friends but i always feel like im the outsider, when i meet a new group of people i never become part of their group, if they are going out, i always just find out and they say come along, im rarely ever invited i have to make an effort. It seems that this eventually becomes the case with anyone i meet new, and my existing friends, has anyone else experienced this? am i just too nice? I always try my best to be helpful and friendly to people but it seems they may be taking it for granted, I just never seem to have any real friends