16 year old male. my stomach very acidic which regularly does not hurt but feels somewhat like fire. could this be asign of ulcers, reflux, or cancer?

Stomach irritation: "acidic" feeling or sharp pains below breastbone/upper midabdomen can certainly be signs of stomach or small intestine (duodenal) irritation (gastritis/duodenitis), an infection (helicobacter pylori), ulcers, and very rarely in a 16 year old, tumors or cancers. If antacids help, likely it's excess acid production, or a decrease in protective mucus (from smoking, advil/aleve, infection). See md!