Just a thought - but is it really a *problem*? If you don't feel sexually aroused when masturbating then can you just not do it?
When I am not hungry I do not eat. When I am not tired I do not sleep. When I don't feel aroused I don't have sex, or masturbate.
Does a lack of sexual arousal *need* to be a problem? I can see where it could definitely be a problem when, in the context of a relationship, one partner wants it more than the other. If that isn't an issue though, I am curious as to why you feel you 'should' masturbate. You say you want to, but if you are not experiencing physical urges to do so (sexual arousal) then where is the 'want' coming from?