I am 21 years old and living with my parents in their home. I am pregnant (if that matters) and they are aware of this and supportive. Today they decided to kick me out due to an argument and gave me 5 HOURS to get out. By law, do they need to give notice so I can find a place to reside?
Sorry, you're legally an adult, and assuming there's no lease between you, you have no right to be in the house except with their permission. You will need to 1) live according to their rules, 2) find someone else who is willing to provide for you, or 3) rent a place of your own.
The Texas attorney who answered your question isn't right.
Your parents have no legal responsibility to care for you after you turn 18, however, depending on the facts, you may still have rights as any tenant would, which would require some period of notice (usually, for oral leases, 30 days).
It may be a question of law, however, as to whether you are a leaseholder (and thus have rights) vs. a guest (with none), which means it's certainly not a slam-dunk case and may be expensive to litigate. You may want to talk with legal aid or another low-cost legal provider.