My boyfriend keeps denying me. What should I do?

So, my boyfriend and I have had our issues in the past but now all of a sudden he doesn't have much do with me. He won't even have sex with me and I've been trying to cox it for three days, but he keeps refusing me and I don't know if its me.... I don't know what to think am I that undesirable, is he that bored with me, or is there someone else? These are the questions that I have asked myself for a month now and its starting to drive me to the point of depression.