Heartburn while running

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I've noticed I get heartburn when I'm running. I've been running more lately than I ever have in my life so I don't have anything to compare this to. If I'm running around a 10 minute mile or slower I'm generally fine, but it can still start around mile 2.5. It's really bad when I'm pushing myself for a 8-9 minute mile after only the first half mile. I don't usually get heartburn unless I'm really hungover and I assure you I'm not running while hungover or dehydrated. (I don't really track water accurately in my diary so don't bother...) I do eat spicy foods, but it's never been an issue for me before.

I run after work, and it's always at least 1 hour since my afternoon snack.

Yesterday was the worst - I was literally concerned I was going to vomit so I had to slow down after 2 miles. Now I recognize that my snack of coffee and Reese's peanut butter cups didn't exactly set me up for success here, but to be fair, I've noticed this when my afternoon snack is a sweet bell pepper and cheese.

I'm thinking about chewing on a couple tums before my next long run unless someone here has a better plan for me to try.