I have been diagnosed with GERD since I was 14 and even though I am only 18 now, my symptoms feel much more severe too. The two reasons that come to mind for me are the long term effects of acid damage and long term PPI usage. Each time acid goes somewhere that it shouldn't, it does more than just cause a little pain. It scars the tissues that it comes in contact with. The esophagus can take a while to heal this scar tissue and other places like your lungs might need even longer to repair itself. As your esophagus gets more vulnerable, the presence of acid has a larger effect on it since scar tissue is weaker than healthy tissue.
This is why GERD is considered a progressive disease, as it causes itself to become more severe. PPIs also play a part in this since they have many side effects that tend to show up after using them for long periods of time.
Right Temporal Lobectomy 4/5/12
Diagnosed with GERD, Eosinophilic Esophagitis, and Epilepsy.
Studying biomedical engineering to research a better fix to at least one of them.