why can't I feel anything during sex? I used to love sex.

Something changed. Did you start any new prescription or over the counter drugs? Did you have a pregnancy scare? Did you move? Do you have any stress, worry or concerns? Are you private when you have sex? Do you lubricate? Did your periods/cycles change? Do you still spend the same time on foreplay/intercourse?

You hint at the fact that it took substantial effort to orgasm previously. I am assuming that you mean direct clitoral stimulation? This is the norm. Women that orgasm from just penetration is the lucky minority by far. Anything that change that amount of stimulation can affect your ability to orgasm.

What changed your experience of masturbation? You say you used to be able to masturbate after sex, but now you feel weird? Did you have a traumatic experience?