Maybe you are trying too hard.. but good for you that you still keep trying..
I remember so well my first attempt at speaking before an audience... it was at school and we were guinea pigging a new exam style - speaking and listening. Our group was the first ever to try it and on the first practice run I spoke about a very serious event that happened to my family.. my fellow students were killing themselves with laughter... and I couldn't understand it...
It turns out that I was so nervous that I was delivering my story in an odd way... that made it seem like a comedian's quips... fast.. short...
My teacher purposely chose me to be one of the small group that went on to trial the actual exam... and I had to talk about another subject... I hated my teacher for a while for that..but I understand now that he did it because i needed practice and learning to speak in front of a group without getting nervous... I still get nervous but I can do it now.
Well funny enough, I am known for always joking and smiling, I make a joke about everything, with everyone.. funny enough too though, I have entirely lost my sense of humour with my direct colleagues, not even a smile is raised with them although several times today they laughed like drains at some very nasty snide joke they made about a student.