I've been through this, Omeprazole at 20mg is a low dose, I eventually was on 40mg twice daily, Lansoprazole is the next step, then Esomeprazole.
In addition it is important to stop eating at least 3-4 hours before sleeping, also to elevate the bed head end by abut 6 inches.
An additional great pill for night time use is Famotidine 40mg at night.
All this is suggestions, and there are no real surprises here, just standard progressive drug use.
This is the advice from a NHS Gastroenterology Surgeon over the past 5 years to date.
Of course, there are many home made remedies, Ie Apple Vinegar etc, but bad GERD Acid Reflux is usually caused by a Hiatus Hernia and that can only be fixed by Proton Pump Inhibitors etc or surgery.