Why am I pretty much not interested in sex?

For a few years now I have had little to no desire to have sex. I don't get turned on with the foreplay that can lead to sex, porn doesn't do anything, and I usually just say in my head "is it over yet?" I've had a couple different partners since I've started noticing it and it's usually only the first one or two times of it being actually fun and enjoyable for me and then after that I'm very disinterested. I like making out and sometimes even with girls too and I enjoy masturbating to give myself an orgasm even when my guy is right there but almost nothing else sexually has grabbed my interest in 4years or so. I've felt this way in relationships and out of them. What is wrong with me?