Spicing things up in the bedroom!

My boyfriend and I have been together for 2 and a half years and for quite some time things in the bedroom just haven't been what they should be ... we don't make love anymore unless I beg for it and the longest we have sex for is half an hour! I am starting to get frustrated because no matter how many times I talk to him about it nothing ever changes! Any suggestions on what I can do to spice things up?