body conscious

I have always been body conscious and worried what boys think about me. I used to be about 20 kilos lighter than what I am now. I used to be in the mood a lot. Now I'm not so much and it's really affecting my sex life with my bf. He always tells me not to worry but I can't stop thinking about it and it puts me off sex as I don't feel sexy. Has anyone else this issue or have suggestions to help me?