You need to be turned on to really get any benefit. I'm about the same if I'm not horny. Enjoying sex and masturbation is as much a mental thing as physical, so fantasizing or reading erotica might help. It also helps if you're wet enough. You could try lube if you need to.
Also, remember your body has lots of erogenous zones that feel good to be touched in different ways. You don't have to go straight for the clit.