On nexium (esomeprazole) for a few wks. forgot to take it today & its already nighttime. does it make sense that i have stomachache and bad reflux? or its unrelated?

Certainly possible.: if you skipped your Nexium (esomeprazole) that day, it is certainly possible for your stomach to produce acid, which could cause reflux in the esophagus. In that setting, it is okay to use antacids for your discomfort. Best, though, would be to try to remember to take your Nexium (esomeprazole) on a daily basis. Prevention of the reflex is better than having to treat it after the fact. Good luck.