Do I Belong Here ??

I have been at my new job for a couple of months and at this company for 3yrs, but I still don't know if I belong here. I seem to be out of place, floating on the sides just getting through the days.

It is not like I don't have work to do and I seem to be doing a lot of it since I spend so much time at my computer doing something but I don't talk to anyone,no one asks me to do anything and no one acknowledges the work I do. So am I actually doing something thats relevant and do I need to do it? My boss tells me I am an important cog to the machinery but I don't seem to get the feeling because I don't seem to be contributing to the show in any way. I don't know how many of you ask that question to yourself but I seem to be doing it on a periodic basis, more often now then ever.