You're not meant to do good things just because God wants you to, you're meant to do good things if it's what YOU want to do! If you do them without consideration to God that makes you an even better person, because it shows that you help people because it's your instinct to do so, not because you are fearful of God. And you shouldn't let God rule your thoughts, or let him be a motive for your actions, God teachers us valuable lessons about love and caring for others, but he doesn't want you to do it because it makes Him happy. God wants you to help others because it makes other people happy. And as for WHY you do things, it's just natural instinct telling you to think on your feet, maybe down to some impulsiveness too, but everyone suffers from a bit of that!
And I also speak before I think, most times it gets me into trouble, but other times it can help. So who are you? You've asked yourself why you do things, there are several plausible answers:
You want to help others.
Your instinct acts for you.
Putting others before yourself.
Impulsiveness.
The list is endless, asking why you do things won't help you find out who you are, because honestly, you'd be very very very very lucky to find out. Instead, compare your actions/thoughts to other people. I use book characters, as fictional characters have very strong personalities, so I'll compare my thoughts/actions to them and if we do similar things then I know our personalities are similar.