And I really don't know that I think that natural cycles of developing natural and ordinary degrees of hunger or thirst should be considered to be "pain.". Seems to me that these are aspects of normal functioning and only situations where abnormal hunger or thirst develops would really be considered "painful.". That goes along with our earlier discussions where some argue that not every unfulfilled desire is a matter of pain.
I'd say by definition that feeling hungry is pain because it's not pleasure to feel hungry... And the feelings are two. In modern neuroscience terms, you either feel positive (pleasure) or negative (pain) affect. It might not be very high arousal in the negative direction if you're just feeling "noshy" but it's negative/pain all the same.