I rock myself to sleep

I'm 17 and I do it sometimes. I don't think it's a bad thing. So I don't see why you need to stop. But if you want to stop then just stop.

This is far more common than most people think. It is usually seen in children at the rate of around 30-50%. In adults it is less common but still can be as high as 2-5% or possibly higher. It may be linked to low serotonin levels and is a form of self-soothing but not necessarily linked to abuse or neglect. It has been linked to repetitive movement disorders but those are usually performed unintentionally. This is usually done with intent.
Body rocking has been observed in infant mammals and humans abandoned by their mothers. It can also be a behaviour trait seen in autism. This does not mean that a person who does this has been neglected or is autistic. A person who does this does get the same soothing effect but perhaps for different reasons entirely. It may have links to a mild form of ocd but it doesn't indicate that the person is in need of therapy or medication. It may have some genetic basis as well. It's not well researched or understood. Suffice to say it's far more common than people who do it think it is. Its not a weird thing at all and doesn't say much about you.

Sounds like a method of self soothing. Were you perhaps exposed to or a victim of some significant trauma in your early childhood?