I have GERD and I have no ins. What is the best OTC medication for that? I already take 300mg of Zantac (ranitidine) a day.

Baking soda. If cost is an issue, and your are already taking 300mg of generic Zantac (ranitidine) a day, then you could occasionally try taking a level teaspoon of baking soda in about two ounces of water for further relief. This is a home remedy that has worked well of decades, but is not promoted in standard medical practice. That said you should be evaluated asap by a gastroenterologist to determine the cause of sx.
GERD. Previcid is a good medication and can be taken with your zantac (ranitidine). If you are overweight, you should consider a diet. Avoid food that make it worse and try licorice (glycyrrhiza glabra.) ot is a flavorful herb that has been used in food and medicinal remedies for thousands of years. Also known as "sweet root, " licorice helps with gerd and a lot more problems. Google it.