Im 17 years old, and I'm pregnant. My parents are iffy about my boyfriend/the baby's father, he's going to be 20 years old and I would most definitely like to move out and move in with him to have this baby, a less stressful environment (considering the fact that I have 3 sisters) and I would feel a lot more comfortable living with him. Is this legal ? Or will I still have to live with my parents? Help !!!!

Depends on where you live. Laws vary by location. A general location will help us try to find the applicable law.

In Florida.

This is Florida law:

Florida: If an individual is under 18 years of age, but older than 16 years of age, a marriage license can be obtained with parental consent. If a minor's parents are both deceased and there is not an appointed guardian, he/she may apply for a marriage license. A minor who has been previously married may also apply for a license. A minor who swears that they have a child or are expecting a baby, can apply for a license if the pregnancy has been verified by a written statement from a licensed physician.

From this site:
Marriage Laws in the US by Age

So it appears you can apply for a license and get married. I would strongly suggest that you not just move in with him as he could get into trouble.

Yes, you can marry him and move in with him after proving you are pregnant when you apply for the marriage license.

Why are the parents iffy? What are their worries about him

My parents will not be able to fight the marriage?
And they are ifffy because he has a record and he's 3 years older.

Sometimes parents know things, before you jump too far into this, why not finish school, have the baby.

If you want stress, living with new husband, baby, most likely on a low paying job not able to do anything

I urge you to reconsider marrying this guy. What we have here is an adult with a criminal record who had sex with a minor. This is a recipe for disaster. A marriage based on this has a very strong probability of failure.

There is also some question about the age of consent in Fl so your parents could charge him with statutory rape.

I would suggest you wait some time and see if he sticks around and shows he has changed before you enter into a marriage that is doomed to failure.