These three are completely interchangable and mean the same thing. 'a little bit' isn't used as often as the other two. It is sometimes used to emphasize that something is small or of short duration, but it doesn't differ really from the other two in meaning.

Examples: 'I love you so much' , ' I think of you a lot'. There is so much violence in the world. There is so much going on. I have a lot of money (I wish):) I have a lot of time.

Almost always, all three of these have the same meaning. Did you have a specific context?