My boyfriend is jealous of anyone I speak to! Help!

I've been with my boyfriend for almost a year now and he's constantly jealous of anyone I speak to. Guy friends, girl friends, even family. I have no idea what to do..I mean, if it was just guys I guess I could put it down to insecurities but he gets jealous when I spend too much time with my 5 year old sister too. I try and give him as much attention as possible but it's difficult. I like to have my space and time to myself as well.
I have absolutely no idea what to do!
I've tried talking to him about it but he doesn't seem to think there's a problem.
Please help