boyfriend not attracted to my body. I need help

Basically my boyfriend and i have been together for 2 years and I didn't sleep with him until almost a year of being a couple because of my own insecurities and because I was a virgin and didn't want to just give it to someone who didn't care love me. Our sex life was pretty active after that but over the past 3-4 months it's kinda came to a stop and felt like I've had to beg for sex, we probably had sex about 5 times in the past few months. I have gained about 20 lbs since we started going out and have thought maybe this was the reason. I know I'm the bigger then most of the ladies he's been with before me. Yesterday I brought it up and simply asked him if we weren't having sex anymore because he's not attracted to me and he said that he wasn't attracted to my body, that there was some attraction but not a lot because I'm a bigger girl. That really hurt. I felt used and ashamed and kinda like he's been lying to me.