Is my habit normal ?

I guess it could be considered normal by some and not normal by others. But on the bright side, you are not sucking on a dick instead.

It's fine, it probably just means you were never given a comparable substitution when you were younger. It's not socially acceptable at 18, but nobody bats an eye if you chew on your nails, drum your fingers, flip a pen, etc. Probably due to the shaming around it people freak out, but thumb sucking is literally just a self soothing behavior. Big deal society, suck on that. If you don't want to get ridiculed, just keep it private or find an alternative.

No, why would that be normal?

Not normal. Stuffed animals, sure, blankets? Why not?
But not this.

I do it too sometimes

how can it be normal if you are the only one doing it?