Could be a couple of things. You might have had these feelings at some point in your life, even when very young and didn't even realize it was happening, and at the time you were either stroking those areas or someone else was and it became a thing for you. Or, for you, those could be erogenous zones. We all have our peculiarities, and there are a lot of very sensitive areas that can cause arousal if one is open to discovering them and then repeating what one discovers. Anywhere, for example, we are ticklish is probably an erogenous zone. I would just enjoy it.